I would CLEAN the mold thoroughly with some carb cleaner, Simple Green, some sort of degreaser. Then preheat the mold by letting it sit on your furnace as lead heats up, or use a small hot plate.

Wrinkles are usually the result of grease/oil in the mold. Or too cold a mold. Or a combination of too cold a mold and alloy not hot enough.

My two cents. Good Luck.

FN in MT