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Try looking for local sheet metal/fabrication companies some may be willing on take on one off jobs but in terms of fabrication if you wanted to even have something done yourself you can look at using a scroll saw to cut out the opening and mark the locations for drilling using a drill press. For $500 that sounds about right for a one off part that require both tool path times and machine time to laser cut and post process. If you have a university or college nearby see if they have a shop that they may be able to have students fabricate sheet metal components.

It looks very similar to the Barrow style of the D5 they aren't considered to be a rebrand of the D5. A real D5 will have a stainless impeller and surround as the pump itself is also cooled by the fluid that flows through it, these are just the same form factor. For the cost if you ware looking for a slightly more cost effective solution a low power DDC isn't a bad option.

Flow isn't very relevant what you mainly want is to look for is pressure as you are trying to force the fluid through the blocks for cooling. If you want a budget pump that's still decent quality I'd recommend to go with something like the DC-LT from Alphacool they aren't the most powerful thing out there but for the price not bad and deemed relatively reliable. It's used in their eisbaer expandable AIO units. https://www.aquatuning.us/water-cooling/pumps/alphacool-dc-lt/dc-lt-pumps/13012/alphacool-dc-lt-3600-ceramic-12v-dc-pump-bulk-version?c=6542

I don't really recommend going really cut throat and getting aliexpress or cheap watercooling components, they don't need to be the absolute best of the best but still get good quality stuff to last. Main thing you want to avoid is mixing metals and get all copper based loop components. In terms of waterblock, and fittings I'd recommend to look at barrow or Bykski as they are more of a budget option while still being good quality and comparable to nicer blocks. For the pump if you want to save a little the DDC or lower power versions like the variants like SPC60 from EKWB are alright.

I'm guessing it's probably some flux or debris from the rads mainly that came out, it's always best to flush and rinse the rads before assembly. I usually recommend to fill them around 50% with just tap water to vigorously shake and rinse, to do that about a half dozen times before giving it a final wash with distilled water. It's probably alright for the time being and you can let it be until the next maintenance cycle just keep and eye on temps to ensure it's not building up.

Was the components mainly the rads properly flushed before assembly? It may have been something also during manufacturing when they assembled the block leaving a film on some surfaces. What are your watercooling loop components?

How long has it been since you did maintenance, usually you want to change fluid every 6-12 months and open for cleaning if there is any build up. Some minor build up or coating of surfaces can occur so you will need to take apart the GPU block and open it for cleaning, before properly reassembling it.

As said that's not really a viable print project nor is it suited to be printed, you would be better off getting it made by a metal or plastics shop which can cut and bend it to shape.

A drain usually drains the majority of the water most times but may leave you with some sections with a front rad with top ports with fluid inside. Some rads a bleed port on the other end which I've used also as a drain in some situations but preplanning the loop for draining is the best. If needed you can place it flat down and move it around to try and move the fluid towards the drain.

Mounting a drive on the back isn't a problem given that there is some space for heat dissipation and it's done securely. I would personally recommend using 3M dual Lock over Velcro as it doesn't let go overtime and try to find a metal tray with a lot of surface area of the dual lock to adhere to.

For aluminum extrusions they are very modular and easy to work with due to the vast number of brackets and adjustability. In terms of tools the basics would be a miter box with a metal hand saw, some files for deburring and the needed mounting hardware to attach extrusions together. If you want to get a bit more complex having a drill and tap for cutting threads in the ends or portions of the extrusions can sometimes be helpful.

Do not mix and match fluids together everything in the propylene glycol will be enough for mixed metal given the proper concentration.

Looks like that is a piece of the threaded block or a section of oring that got sliced, I would personally replace it especially if it's very flat from extended use. I personally replace all the orings in the fittings every 3 years or so. Those bitspower ones are good I've used those before.

I'd go with the tried and true method of using ethylene or propylene glycol as it is what is they use in the AIO's originally.

I would give it a slight turn to see if it's loose to tighten it down on the block but don't overdo it. If it's still leaking you might have a bad o ring between the compression fitting and block which can be replaced. It would need to have the loop drained to do so.

It may be possible but probably more hassle than it is worth, you could always get a similar for factor case with the added cost and time to modify the current one. https://silverstonetek.com/product.php?pid=536&area=en

Oh they're way past any kind of warranty at this point that one was an old block, the issue I found was the screws were heavily over torqued from factory compressing the actual acrylic. The only reason they cracked was due to the removal of that stress and opening the block during cleaning. I had a similar issue happen to a CPU block like with OP but spider like lines which they were able to help me source a new top section.

Simplest would be to take dryer sheets that have the static reducer and to just gently wipe down the panel. in commercial applications we have static sprays or ionizer bars we pass materials under to reduce static clinging.

As others have mentioned you are best to check during maintenance of the loop to take it apart and verify it's integrity. From the looks of things that looks like a scalloped failure and will require a complete top replacement. Minor hairline cracks can also form from stress overtime or even happen after you remove the top and let it sit due to the sudden change of the stress in the material. I've had plexi tops form tiny spider like cracks under screw holes right in front of my eyes when releasing that long term stress. Minor hairline cracks can be touched up but ideally should be replaced.

Even with corrosion there isn't too much to worry about as long as the sealing surfaces are intact, being a pure copper base there is less likely hood of that occurring given the proper additives. I've got some now 6 year old blocks that are plated with heavy nickel corrosion due to age and just wear from waterflow from running a lot of pastel fluid over the years and while they aren't as nice looking they perform exactly the same as when they were brand new.

I've always gone with a mix of <50% isopropyl and distilled water for cleaning monitors for sensitive surfaces. Most times a damp towel is enough to get most stuff off.

Never heard of the plugs being an issue but if it is a concern you can always get replacements.

-Moved to new Builds and Planning-

-Moved to Case and Power Supplies-

Places like Cold Zero make custom acrylic parts and has some options for extended PSU shrouds. https://www.coldzero.eu/search?controller=search&s=h500