Yeah, you don't want to use an oiled gauze filter like K&N. They are only the rage in diesel truck places where ignorance abounds. Cummins and now GM recommends against the use of oiled gauze as the filter plain lets more dirt and oil through. Enough to damage the turbo and foul sensors. The k&n type filter, there are many copy cats now, are a high flow performance filter. Whenever you let more air through a given area of filter media, you let more bigger dirt through.
My vote is for an air filter restriction gauge. You will likely discover that your dirty filter is not too dirty yet. The next step is a large Donaldson style cylinder filter assembly and filter. These filters are larger with more surface area so that they can collect more dirt before creating restriction. They are paper like OEM and don't have bigger holes like the K&N so the chunks of dirt will stay on the dirty side. 81$ is alot. I think you will find that the replacement donaldson type filter will be much cheaper and last longer. You will come out ahead before long.
The diesels suck in mucho air. The diesels is tractors suck in mucho dirty air. With such tight clearances in these engines, a good supply of highly filtered air is important. Don't go K&N and do use a filterminder restriction gauge.
