If you still have the OEM mechanical fuel pump, the rubber diaphragm splits/deteriorates (especially with ethanol gas) and gas will bypass it directly into the crankcase. Fix is to rebuild with new gaskets/diaphragm (newer ones aren't rebuildable) or go with a rotary electric gas pump.
Also if you park on an incline with gas tank higher than the fuel line/carbs, it can leak if needle valve/float is the least bit leaky. Many add a manual fuel shut off valve up front under the tank to shut off all flow when being stored. One from ACE HW for a lawnmower works fine. This will prevent fuel smell and fire hazard when parked for winter - if stolen it won't get far either.
I would drain and refill the oil shortly as one change won't get all the gas out of the engine. Gas is not a good lubricant for bearings. Get a good fire extinguisher for peace of mind!