I'm replacing my motherboard and just want some general advice. I've put new CPUs into new motherboards, but never a used one. Should I put new thermal gel on? Do I need to scrap off all the old stuff?
Don't scrape it, just wipe it off. If you scratch the surface, you will be dramatically reducing the cooling efficiency. Use take a coffee filter (or any other line-free cloth) and get some rubbing alcohol on it, then just go to town. It comes off very easily.