Motorcycle Questions? Ask a Mechanic.
Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially and I am aware that the petcock has been ruled out, but re-check even if to eliminate the possibility of a vacuum leak.
Fuel flow from the tank only passes through the petcock. From the petcock, it has three (3) potential cause of the "...gas leaking into oil..."
Since the carb and the petcock (vacuum valve) has been ruled out, then by process of elimination, the only potential suspect left would be the fuel vapor separator system.
Check the air box enclosure and air filter for sign of raw fuel