Isopropyl Alcohol usually does the trick. Don't need to use a lot either, just dip a cotton bud into some and gently rub it over the affected area.

PTherapist wrote:

Isopropyl Alcohol usually does the trick. Don't need to use a lot either, just dip a cotton bud into some and gently rub it over the affected area.

Yes.

If need be you can use a soft toothbrush to initially break it up and follow that with the cotton buds or swabs.
Wooden toothpicks can help to break it up too but take care not to dislodge any SMD parts.
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you also might have to remove the metal spacer on 9500-9800 series Radeon cards to get thermal contact with regular thermal paste.

I have a 9700 pro, where that was an issue, the metal spacer is higher than the die.

Looks like I'll be going the pharmacy tomorrow then! I did try holding it under nearly boiling water to see if it softened at all, but it didn't 🙁

If you can get 90 or 91%. Works better because less water.

WD40 also cleans well this sort of mess. Apply it to the silicon die and the dirt pcb substrate with a cotton swab, wait a bit and before it dries, clean with a kleenex or other soft paper.

With a steady hand and a small flat tip screw driver you can easily remove a lot of it from around the core without damaging it however for the think film of it on the gpu core you need to use 90% or better Isopropyl Alcohol, don't bother with cotton swabs as they suck so use a normal cloth instead so you can safely scrub the surface without causing harm. Finger nails if you got any can be handy for little jobs like this then clip after.