Rebuilt this 2002 400ex, probably put 20 hours riding on it since rebuild. Noticed when putting it away yesterday that it has a leak at the base gasket. It will leak really slow, when Reving only. I wiped it dry and let it idle for 5 minutes no leak, throttled it and can see the oil bubble out of that gasket. The head gasket and tensioner gasket look good, is this something I need to tear the quad down and replace? Is that a common gasket to go bad?