I used M-F plastic for several years along with RTV molds, aluminum, resin, etc. I've never had the problem you are encountering. I never heated nor washed any of my rtv molds and had some that were about 20 years old. Could heating and washing them be the culprit? The only thing I did to rtv molds prior to pouring , was to apply a little worm oil or scent with a sponge brush to get a shiny finish on my baits.