these bikes have no oil tank, but if fuel is entering engine oil, i.e the crankcase, then you likely have both a leaky fuel valve, which should not allow fuel to flow unless engine is running, as well as at least one leaking float valve out of four float valves,,,one for each carb. both are fairly simple fixes, and cheap as well. if fuel is getting into your COOLANT TANK i.e. behing left plastic body panel, you have a blown head gasket, or similar deep issues that require major work.