I have bought several various vehicles for looted wagon conversions. They were all painted particularly badly. A litre of dettol in a bucket, throw in the vehicles and add water till they are covered, with a weight (brick) to keep them under. I left mine for a week or so and the paint turned into a greasy sludge that was nigh impossible to clean off with water and clogged any brush that touched it. But I did find that it was easy enough to use a brush in the actual solution to get the goop off.
The dettol had no effect at all on the plastic apart from leaving a very pleasant smell.
For metal minis, I couldnt agree more with the brake fluid approach. Dont disassemble, just put them in a cup and top it up over their head.
Ive also tried dettol in an ultrasonic parts cleaner with good effect on plastic models. But by no means put a metal figure in a lapidary tumbler :-D Unless you want a shiny blob shaped piece of metal.