austin86
This could be died out flux residue that dust has sicked to or remnants of the chemicals used when making the PCB. I seen this on a lot of older cards. No real way to remove it without risking harm to the card.

I removed most of the dust and grease with a dry cloth and brush, very carefully so as not to damage the board components. When most of the dirt was removed, I treated everything with alcohol, removing residual oil, blowing air on places where dirty alcohol could remain and dried the video card with a hair dryer.
The most painstaking, these are the places where dirt could get under vram components, or chokes.