Discoloration on GPU PCB

[dirtychaps]

Howdy yall. Going through a much needed cleaning on my PC as well as some upgrades and came across this dark spot on my gpu. The oil isn't the part in question, well aware that that is just oil from the thermal pads on the pcb, but the dark yellow spot and just overall browning of the PCB seems strange to me. It's heaviest around the actual connectors. Anybody know if this could be from the oil as well? I have recently ran into issues with thermals in general lately, hence the reason for the upgrade (swapping out case fans, as well as adding others). Just want to make sure the gpu isn't cooking itself.