I had my 2006 mercury 4hp stroke stored in the garage over the winter and noticed a fair bit of oil had leaked out the propeller- again. It does not appear to be gear oil, its too light and it's blackish. I suspect it's engine oil turned dark by the exhaust soot. I originally figured it was gear oil and bought a new seal. I drained the oil but there's not a trace of water in the gear oil. Lower crankcase oil seal? How difficult to change? Hopefully easier than the lower unit oil seal.