Gas in the oil is a really bad thing, dilutes the oil and causes bearing failure. So get that changed with a new filter. Use 10-40W JASO MA rated oil, automobile oil will not work with the clutch.
Once that's done clean the engine with a degreaser found in auto parts stores, follow the directions. Once the engine is dry throw some baby powder on the suspect areas for leaking and run the engine for a few minutes. The powder will turn into a gooey mess where the leak is.
Do you have the FSM, factory service manual?