Method and apparatus for molding a sealing surface of revolution on a molded part in first and second partable mold halves that mate at a major parting line plane. First and second mold inserts each have a sub-insert trim wheel component shaped to mold form the sealing surface of revolution when closed at a minor parting line plane. The sub-inserts are rotatable between a position flush with the major parting line plane and a starting position angularly offset therefrom. The mold cavity is filled with liquid molding material that is allowed to harden to at least a self-sustaining solidification strength. The sub-inserts are then rotated to thereby move any minor parting line flash toward a position angularly offset from their starting position. This rotation causes any parting line flash that might otherwise remain on the sealing surface to be removed from attachment to, and/or smeared smooth along, such surface.