Not a Harley expert by any means (but learning, as a Low Rider owner) but the M8 engine has a dry sump lubrication system so, theoretically, the (separate) oil tank could be overful as the oil pump transfers the oil to crankshaft etc, then falls into the crankcase area, where the scavenge pump will push it back into the oil tank. Therefore, the oil tank level shouldn't be an issue, unless badly overfilled. A wet sump engine, if overful, could find it's way into the crankcase breathers (helped by normal crankcase pressure), then up into air cleaner. However, some M8 engines haves suffered from "sumping", where the oil in the crankcase is not scavenged quickly enough, which could lead to breathing system oil overload. I have a suspicion though, that your situation is normal.
There are far more expert HD riders/owners than me on here, so maybe you may get some other feedback.
