Leaky Radials
Don't think I ever encountered an engine which came even close to leaking as much oil as a Bristol Hercules Sleeve Valve. On manufacture joints were metal to metal, which was fine until some boofhead split components by driving a screwdriver between the surfaces. Even buckets full of Hermatite sealer could not keep the oil inside the engine. First action by the groundies when the aircraft stopped on the ramp was drain bucket under the nacelle drain tube and then the chocks in place. With sleeve valves to be lubricated plenty of oil also made its way out the exhaust ports. We jokingly called them "High powered Oil Pumps"