I have a Toro single stage with the rubber auger and for the money it cannot be beat. Last winter we had 2 feet of snow and it worked great. The only downside is they are 2 cycle.
My dad has an Echo generator with a Robin engine. It has 2,000 hours on it with only oil changes, spark plugs, and air filters. The engine has never been touched.
I don't want to ruin you day, but when the intake gaskets started leaking in my S-10 at 33,000 miles the leak on the garage floor was about the same spot a water pump leak would be. If you make enough noise GM will pay for the repair if it is the gaskets.
You might want to drain the oil after you mow and then change the filter the next day after it cools off. Any oil left in the filter would be "thicker" and not as apt to run all over the place.
I can GUARANTEE you there is not 5% fuel in the oil after a race or they would never pass the oil test. AND the guys setting up their carbs are tuning for gas mileage so I'm sure they are not errantly dumping fuel in the crankcase.
I had to have the intake gaskets replaced in my 99 S-10 4.3 at 33,000 miles. The mechanic, who is a good friend of mine, recommended I get 2 gallons of regular Peak antifreeze and he would flush the system and install it after he did the gaskets. He didn't have too many kind words for Dex-cool.
I have a farmer friend of mine who uses Cen-Pe-Co 15w40 oil in his vehicles and changes it every 10,000 miles with a Fram filter. He had a Rabbit diesel that went 290,000 miles till it died and a Nissan Sentra that went 246,000 before the frame rusted thru, but the engine ran fine.