Also applies to P4s. May be a duplicate post....Recent presentation (well, last year) at club meeting by a member was on air cleaners, based on experiences whilst he worked with a large US company that made big industrial vehicles and equipment. Company did a major review of air cleaners , prompted by customer complaints about short engine life between major overhauls. The upshot was a complete switch to paper filters from oil bath types - VERY large improvement in engine life. Being a very long time owner of a P5, he now runs a paper filter inside the std oil bath canister. Re paper filters, he warned that one should NOT either vacuum the outside, or blow air through the outside.