Hi, My son has a 80 633 and has a oil leak at the back of the head.WE changed the rear main when we did the cluch and also the gasket on the back of the head.The oil sender is also new.Could it be the head gasket?The car has over 200k on it and i'm going to do a cam and valves this summer.Any help would be greatly appreciated. Thanks Chip 80 633csi 85 635csi