I use Clean-Rite "Purple Power". It sometime takes awhile but is less hazardous than some other strippers (like brake fluid) that I have used in the past. Heres a model with a 50 year old paint job which took 2 sessions. First two pics are after 1st soak, next 2 are how nicely it cleaned up after bath # 2. The hardest paint to remove was the brushed on black Testors PLA in the engine compartment area.