What causes gas to get into the oil on a 13 commando kohler motor in a john deere?

My Kohler carb had a bad needle valve that wasn't stoping the gas once the bowl was full. I bowl filled , then gas kept coming so it ran into the cylinder and down to the crank, lost a full gallon of fuel. I would recommend that you start by dropping the bowl and testing the float and valve. Flush you crank case twice with oil after you have drained very bit of the contaminated oil. If you want further instructions let me know otherwise I'll assume you know how to check the valve.

You can have a microscopic particle of rust, or other "trash" in the fuel and it can hold open the needle valve. Thus allowing for the flow of fuel into the carbs fuel bowl, flooding it, and going through the intake to the cylinder and finally into the oil. You can remove and clean the carb. And install an inline fuel line shut off valve and help prevent this in the future.

Makes sense

Correct answer, similar to the previous