you won't always see any oil leakage, I had water get in my lower unit and caused it to lock up tight. had to replace it. now if mine sit for a while like for a couple bad winter months. I'll loosen the drain plug to see if any water comes out. and I change it once a year. remove prop and clean good, smear a little grease on shaft. replace prop and torque at 50 ft lb. " Mercury engine "