if it's the outer case, try taking the side case off...and see if most of the gasket is still on the case/motor..if so..get some hondabond..or yamabond..put some of this on the spot where it's leaking....try not to put alot on it..you don't need much to seal it..put it back together..it shouldn't leak anymore..as for a gasket period..i've used alot of after market gaskets..and never had any problems.