I need to make a membrane for a brake. Printed one out of TPU, mostly to check for tolerances and didn't expect it to work, it indeed does not and seeps the mineral oil through. Now my plan is to make a mold and cast one out of RTV, but even with the draft angles and supposedly slippery PETG it just glued the mold shut and ripped up in the process of opening it back up, understandably so because layer lines are grabby. Do I 3-piece mold, or do I do some kinda release agent?