Was the sender leaking from day one?
It seems likely. The breather is always a possibility, but on a new bike there should be a plug in the drain line (these seem to eventually go missing) and there shouldn't be very much to see. Since there seems to be no common oil level that works for every bike, it's always possible to slightly 'overfill' (for a particular bike). However, there have been many bikes, both large and small block, that have had leaks at the oil pressure sensor, the phase sensor, etc.
