Is he sure it's coming out of the area around the air filter? Not the oil filter?
The air filter sits in the air cleaner box above or next to the top of the engine. The air cleaner connects by a hose to the carburetor.
Here's a schematic of the carb, if it helps him in any way:
2003 Eiger Carb
If the oil truly is pushing into the air cleaner, I'd take it to the dealer if it's still under a warranty.