As others have said, that's completely normal even when running. But leaving fuel in an engine at the end of the day is not a good thing, that's how rust starts. At the end of a day's flying, always run the engine at full throttle (preferably) and either remove or pinch the fuel line and wait until the engine stops. If you've pinched the line then hold it for a few seconds after it's stopped to let any tank pressure bleed back through the muffler line. If you've removed the line then pinch it as well or it'll spray fuel everywhere from the muffler pressure. Doing this will get rid of all the methanol but still leave lots of oil coating everything. If you've got castor in the fuel then it's also an after run oil. Empty the fuel tank as well because it will gradually absorb water from the air and may give you problems next time you go flying.