Those twin engine like the onan and Kohler when they need to be rebuilt it best to do it before you break a connecting rod, They have a tendency to break the cam when that happens, I know of some Wheelhores tractors that happen in and the cam around 200 bucks the last I new. But they do have preasure lube, so If some has been good with changing the oil and filter as need, they will run a long time before a rebuild.