[munter]

Did you cast them, Gordon?
Did you use release agent?

After a good scrub and chemical clean if  areas not taking paint still is a problem I think it is a resin issue not a release agent issue.
One part of one type of resin I use starts to crystallize after some time and I think if this is used on making bodies I think parts remain unmixed and cause this issue.....No empiracal testing sorry, just a gut feeling.

Solution is to.....find a paint that works or....there's the bin over there.