Hi
Is this a 2-stroke or 4-stroke engine?
On a 4-stroke it could happen, gasoline is running down the cylinder walls if mixture is way to rich.
But then will notice gas in the oil ... just a few millilitres so to say.
If it is a 2-stroke, gas and oil will be mixed before entering the cylinder, I think, and I would have a look if there 's a broken valve or something, so that gas can run down the oil line, if the engine is off.
Regards, Stone