Thin oil is a SYMPTOM not the disease.
The fuel gets in there because the float is not completely shutting off the fuel so when not in use fuel overflows down into the cylinder then dribbles past the piston & into the sump.
You really need to fix the actual problem which is the carb.
I understand that. I have a shut off valve that i closed and let it run the gas out of the carb bowl. I stored it all winter with the valve open. When the weather warms up here in Michigan I will look at the float and needle.