K&N kind of got the market cornered on the rag paper filters and the animal/mineral oil blend they use to oil them. They charge a tidy sum to buy their oil and filter cleaner products as well. They are very efficent filters but at a price. The rag paper does deteriorate and given time, it will need to be replaced just like a wood pulp paper filter would.
If you use a light weight oil in an oil bath filter, say 10 or 20 SAE grade, it will slow the airflow less than a grade SAE 30 or higher. As was mentioned earlier, the CFM flow rate should be completely adequate for a stock L-head engine. If you want to make K&N wealthy for the small amount of performance gained, then keep buying their products but the oil bath is more efficient through a full 2000 mile run than any type of paper filter. The paper slows down CFM flow pretty quickly after it gets a lot of dirt in it while in the oil bath, the dirt settles to the bottom of the reservoir and the CFM flow stays the same.
My 2 cents.
Kerby