Liquid Ultra does definitely stain the CPU and a nickel plated heatsink a little bit. I tried it on my old A64 3200+ (unlapped) and a nickel-plated Thermalright XP-120 for about 24h with Prime. Using just isopropyl alcohol and a cloth is definitely not enough to get it all the stains off. It only stained the surfaces though, similar to how untreated copper stains when you touch it, there was no bonding noticeable, and no hardening of the paste. I will have to try and make some fotos where you can see the effect and then try Nevr Dull to see if that gets the stains off without getting rid of the model markings on the CPU, but I haven't gotten around to it yet.