DOT 3 brake fluid, castrol super clean/purple power from the dollar store, simple green, yellow can oven cleaner. all require an amount of soaking time and elbow grease.
what kind of paint?
How was it applied? (brushed,sprayed,dipped)
any bodywork/filler?
did you use a primer? if so what kind/type?
with the answers to these Questions we can better give you the best method.