Dot 3 brake fluid and Dettol work for me on both metal and plastic miniatures with no loss of detail / softening etc.
I have tried both alone and have left models in for several days at a time with no adverse effects but have developed a technique that works for me:
1. Place models into brake fluid for a few days then scrub with a toothbrush (you need to be fairly forceful, but not enough to damage the minis).
2. If this removes all of the paint then give the models a good wash in warm soapy water with more brushing and they should come up like new go on and paint.
3. If you don't manage to get all the paint off with brake fluid, try washing the models as above and rinse well with clean water before placing them in Dettol for another day or two.
4. Any remaining paint should then scrub off fairly easily, then wash again as per step 2 and you're ready to paint!
My reasoning for this method - Dettol softens acrylic and enamel paint to the point that it can go very gungey. This makes it difficult to remove efficiently without gumming up your cleaning brush. Brake fluid breaks the paint down more evenly without softening, it appears to almost "absorb" the paint into an oily film that scrubs off nicely but can leave a coloured residue; this is where the Dettol comes in as it can soften the paint stuck in finer details and make it easier to remove once most of the surface paint is gone.
Just my 2p worth
