Oil on a filter is used to trap fine dust. Oil on a foam element will stop water and mud. Paper filters stop dust. Depends on the filter. Any air filter that cuts horse power is too small(not tall enough or to small around(surface area is too small) Dust is an abrasive(not what you need to keep any engine alive) To oil or not...depends on the conditions(lots of dirt roads on your trek?) and the maker of the filter. K&N uses a non woven material. Lots of fibers, and air will pass well. The oil they use closes the random gaps that are in that kind of filter. Some paper filters will dissolve with oil. Not good. Mesh filters(like our oil bath types) last a long time, if you clean them once in a while.

Steve H