Honda Express L-Crankcase leaks

[Kroozen]

I just bought a 1978 Honda Express that has not run for about 10 years. The moped runs and idles great considering it sat for so long. My question is than when it sits and idles after about 5 minutes the L-crankcase will start leaking oil. The oil appears to be coming from a vent tube that starts on the back side of the case and folds under the bottom pointing out. Is the crankcase over filled or is the gasket problay bad?
Thanks for any help