A cheap and good test can be done to let you know what may be wrong with your engine. Take an oil sample to a Speed Co oil change facility or any of the larger truck stops and have them do an oil analysis. By the various chemical in the oil they can then tell how bad the rings, bearings, valve guides, and seals are. Or if it has gasoline is in it. Remember, on automotive style
fuel pumps, if the diaphram is leaking the gas goes on the ground. On marine
fuel pumps, if the diaphram is leaking the fuel goes into the oil. They can also tell you the vescosity of the oil at the time the sample is taken and it's acidity. This will tell you if the oil has broken down and if you really need to change it now or can wait longer.