I normally clean my GPU and motherboard with 91 percent isopropyl alcohol but it leaves an oily looking film even though the bottle says the inactive ingredient is water. I found some MG Chemicals 99 percent anhydrous isopropyl alcohol on amazon but I’m wondering if its safe to use and if it will leave the same film.
In my personal experience, I've found 99% more effective for cleaning CPU thermal paste, especially when complemented with a surface purifier. Arguably if I'd used 91% i'd have experienced the same CPU performance without any additional heat but I'm not going to shell out on some 91% when I have some 99%. Also, make sure you use a lint-free cloth when removing thermal paste.