After flying, I have opened the oil filler and observed smoke coming out. Is this just hot oil vapor or possibly water vapor? Would it be advisable to always let this vapor vent after flying? It last about 5 minutes on a 320 Lyc that burns no oil. On another front. Should one consider putting a rubber ball in the exhaust pipe to block raw air from getting in the engine? If the engine stopped with an exhaust valve open then atmospheric air with plenty of water vapor could enter the cylinder. Same thought with the breather hose.