I want to say you're meant to oil those filters. Mine is K&N bit I have a pipercross clean/oil kit.
I fired off a quick email to Pipercross for some confirmation, here's the reply.
Many thanks for the email.
The PP52 is an impregnated filter meaning it is oiled, this is vital to the air intake system as it improves the airflow but not only these captures smaller particles which can cause harm to your engine.
Once you clean this filter every service or 10,000 miles we would strongly recommend re-oiling this again.
So in short, it's oiled from factory, so fit and forget till the next service