Replacing the air filter will not cure a turbo oil leak.

If the car is under 5 years old its still under warranty if you have a full service history using the correct parts and all the receipts.

Simple fact is the leak will not get any better and will eventually need sorting, your call.

I get where Skidpan's going, was the last service at or around the 5 year anniversary?, if so and they advised the oil leak at the time then it should be fixed under warranty.

If the last service was after the 5 year point and they won't play warranty ball, then a decent indy could remove the turbo and get it overhauled by Turbo Technics or similar, but you might lose the car for up to a couple of weeks whilst this is done, depending on how common the unit is an exchange one might be a better bet re time scale, whilst yours is just leaking but otherwise ok it's a good exchange or fix bet.

Thanks for advice