keithahlstrom, That air filter's oil wetting can be caused by 1 or more of these things:
1--Over filling the engine oil.
2--Tipping the Genny on its side to drain the fuel tank.
3--Having the Genny tip over, even briefly, during road transport.
4--Really Over-Using the Choke on start-up!
5--Running very near the rated Wattage output in hot weather for 15, 20, 30 minutes plus, especially when combined with a little bit of item 1 above.
My guess is either 1 or 5.
FYI, everyone should always shut the fuel off 5 minutes before desired engine shut down, especially before moving it or for vehicle transport. If you do not, tipping it with the fuel ON will allow overfilling of the float bowl enough for fuel to run into the intake port and very likely into the combustion chamber where it will slowly leak past the piston rings and mix with the engine oil. That can/will raise the oil level as it dilutes and thins it out, causing the engine to run over-rich while degrading the oil's protection.