John Deere riding mower model STX38 is getting gas in the oil. I drained the oil and it smelled of gas and had the density of gas, not the thickness of oil. Any suggestions as to how this is hapenning. I can change the oil and put gas in it and it runs great for some time.

Hi,
You did not say whether it was a yellow or black deck, though that would only serve to give me a rough idea of the age. At any rate the inlet seat in the carb is worn out, a common problem with that family of Kohler engines at that age. The best cure is a new carb; you can replace the inlet needle, but that usually only proves to be a temporary fix that will not finish out the season. The other cure I have seen many times is to put a fuel shutoff in the fuel line going to the carb and to use it "religiously." I cannot begin to count the number of STXs I have seen with that added.
Peace,
Clarke