What you have is a governor shaft seal leak, a fairly common occurence. Part number is 92049-7019. It can be replaced without removing the engine. Control plate has to be loosened to allow governor arm to come off of the governor shaft. Unless it has been replace with hi-tack it can usually be removed with a couple of small picks. Avoid scarring/damage to the governor shaft. Governor will have to be properly set when governor arm goes back on. You can search this site for instructions--Rob has posted them several times.
Apparently, as Rob has suggested, your carb has picked up some trash that is holding the needle open and gas has run through the intake, past the rings and into the crankcase. Could also be a defective inlet needle. The thinner gas/oil mix has made it easier to leak past the seal.
Once you get the carb problem taken care of and the crankcase refilled with the correct amount and grade of oil, you may still have a leak but likely slower. Had you noticed any oil on the equipment below the seal area before you encountered the overfill?