I normally leave my laptop on a cooling pad (these hard gel packs that absorb heat, actually it works pretty well for a passive heat dissipation solution) and picked it up yesterday and noticed a bunch of white residue on the cooling pad, which was also all over the large removable panel (where the hard drives and memory can be accessed from). I checked the cooling pad for damage, but found none (other than it had been leaked on). I opened the panel and couldn't locate a place the substance had come from on the circuit boards.
After thinking more about it, I wondered if it could have been thermal paste from the GPU? it didn't appear to have leaked out of there when I had looked, just the positioning made it a suspicion. I have never replaced the GPU thermal paste, but know how the procedure would go (even have the tools and materials to do it).
But before I disassemble the laptop to chase down this issue (which I still cannot locate a source inside the laptop for), I thought I would post in here and get some other opinions. I wish I had taken pictures before I cleaned it up. But it certainly looks like thermal compound (although much more runny, given the way it leaked.