Fuel in oil

Many over the years have had this happen and it is usually a limited time issue. Are you using 91 oct. auto fuel or 100LL? You can drain all the fuel including what's in the lines and change the oil. My bet is it will go away.

Roger, what is the theory on why this happens and why it goes away?

Im using 95 oct, auto fuel. 

What cause it?

Why do you think It will go away?

I have done a little research and testing and from what I have found was diesel fuel in the auto fuel and it migrates towards the oil. Not sure about the why's, but seems to happen with auto fuel and someone at the pump tanks didn't flush his hose before dumping in the auto fuel tank after the diesel. I don't think I've seen this with 100LL because it never gets close to diesel. So if someone knows more please chime in.

There are two ways to get gas in the Oil.

The least likely way is for an old style fuel pump (that shouild already have been replaced) to leak into the crankcase.
Not very likely.
. . .
The more likely cause is that a hight wing plane was parked with the fuel selector valve in the ON position and the Float valve in one of the carbs does not completely seal perfectly.
The float bowl eventually overflows into the carb throat and the fuel dribbles into a cylinder that just happend to stop with the Intake valve in the OPEN position.
The fuel settles on top of the piston and seeps past the piston rings into the Crankcase.
The first time you start the engine or just "Burp" the Oil tank,  all the fuel in the crankcase is transfered into and overflows the Oil Tank.
The luck of the draw causes this to be an intermittent issue as only one cylinder stops with the intake valve open.

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And another reason for "Burping" the Oil on the first flight of the day.