Oil Leak

I have a oil leak that I can not find on my Roketa 167fml 200cc engine. It seems to come from the front sprocket cover ,but when I pull ithe cover no oil. It started after an oil change, so thinking it was the oil screen cover, I drained the oil after a ride and re-assembled the cover. It's still leaking. No visable leak higher up. Anyone had a similar problem with the 167 engine? Maybe a quarter size spot on cardboard, but with 600 miles on the engine I didn't expect this.