Replacing a heatsink on your NVIDIA monster? The compound that’s on there might be a mess. Also, it might have migrated around/underneath memory chips, wreaking havoc along the way. Wiping the stuff just gets it all over your fingers and messes up a good microfiber cloth (since paper towels tear and other cloths leave lint).
Acetone and rubbing alcohol mitigate that a bit, but leave something to be desired.
The real solution is Goo Gone or Goof Off or a similar product, and a toothbrush.
Pour the Goo Gone over the ram chips and/or GeForce core, and use the toothbrush to scrub them clear of the heatsink goop. Rinse with water, making sure not to allow the goo to drip onto the other side of the card, and allow to thoroughly dry (24 hours) before reinstalling heatsink.
And for deity’s sake, use less goop next time! It does NOT take much.
You can use the same technique to remove goop from the cooler’s heatsink. I recommend removing the heatsink from the cooler first, because when you wash the solvent + goo off the heatsink, it has an uncanny attraction to plastic and will end up coating the plastic housing of the cooler with a sticky, cloudy layer. It doesn’t affect cooling but looks terrible.