While we're on the subject of oil, my avatar is a picture of an Onan 14 hp horizontal shaft with right at 600 hours on it. That was the second time I had it apart for the same reason, which you can see at the bottom of the sreen, is a gasket sucked in in the exact same place that it happened before. The engine now has 1100 hours on it.
My "fix" to keep it from sucking that gasket in was to clean the foam wrapper on the air cleaner every 10 hours as recommended by Cub Cadet, not every 50 hours as recommended by Onan.
This repair is described in a post in the Cub Cadet section a few years back.