I've been told to soak my gas piston in CLP overnight... but I don't have the patience for alRSE+Ml that (and my wallet isn't big enough to squirt that much CLP into a cup to soak my gas piston). I pretty much have to pay $4 in CLP every 2-3 cleanings because I run out.
For my gas piston (the most stubborn of which to clean), I use Brasso + some elbow grease. It does the job faster and cheaper than CLP.
After doing my corrosion test, I just pulled out my stockpile of cheap ATF that I use to lubricate everything in the house, car, garage, etc... Try it on your car door hinges and trunk torsion bars.
Supertech ATF is about $1+ change for 1 quart. For my RPK, a quart will last me at least a year. For general cleaning, I have my mix of ammonia, alcohol, and ATF as well as WD-40 (note, I do not use WD-40 as a lubricant or preservative because it sucks at doing both). WD-40 will take off adhesives and other gunk, but since its cheap and plentiful, I use it to spray off primer salts stuck to my FCG and other nooks/crannies in the receiver.
But until I find something better than cheap Dex3/Merc ATF, I'll be using that as a cleaner, lubricant, and preservative.
If I had to take a guess, ATF would fail MIL-PRF-63460D in the skin irritant test. A lot of people are will break out in hives/rashes when in contact with ATF. It contains a lot of petroleum distillates 80-85%, and a lot of dispersants (that perform the same job as detergents).
Pouring tranny fluid on hot metal objects will just result in a lot of white smoke. I seriously doubt CLP, Militec-1, Firepower-10, and other marketed products will react differently since they're all petroleum based products... so the concern about fires and what not is probably minimal.
The funny thing is, Mercon-V, a Group III synthetic ATF, did not perform so well in my corrosion test.