Thanks everyone!
I wasn't expecting so many advises. Although i'm an IT, I didn't expect to encounter these kind of problems. Though I should say that I am pretty new to water cooling.
I must admit, I didn't think of the tooth brush and I'm pretty sure it's going to work. Regarding the pump, I've never disassembled one nor a CPU block but I am pretty confident it will go well. As for the Rad, I Will try your tips so i can clean it back as much as I can. And for the record, I am not buying a new rad. it is not done yet even if it needs a bit of love.
While I am here, would any of you know a transparent liguid that would be good in my case?
Thanks again,
SergentRoux