Warranty and watercooling

[ddd1]

So my goal is to add my 7970 and 7950's to my custom loop.

Obviously this voids the warranty, but the cards have no warranty sticker.

I think the only thing they can notice is missing thermal grease as when you remove coolers I know from experience some of it gets stuck on core and is difficult to put back on the cooler..

Do you guys think they look at the thermal grease?