I have a Scott push mower which has a Briggs & Stratton 6.5 HP engine, model # 121602-0121-E1. Oil is leaking out of OHV to the deck. I took the OHV apart and found about 1/8 to 1/4 oz of oil in it. Is the amount of oil normal? If it's normal, then, I guess it's the head gasket that's leaking. If not normal, what gasket is leaking?