Dot4 brake fluid.
Put it in a plastic container for a couple of days minimum, with models fully submerged.
Then rinse the models under running water and scrub with an old toothbrush where necessary. The stuff won't eat the plastic but loosens paint and glue bonds.
Just don't let it touch your skin, and dispose of it in a correct manner; as chemical waste.
Alternatively, if you're in the US, use a cleaning agent called Simple Green: it's the best I've ever used. It too is safe for plastics and better still; it's environment friendly...