I have just changed the oil and sump gasket on my Suffolk Punch engine, Type 98G14. Model No. 3A. The sump is held to the engine body by 2 hexagon head set screws. At the sump plug end, the set screw holds down a round cap, about 1 1/4" in diameter. Can anyone tell me what the round cap is for? And what type of seal should be sealing it?