Just to clarify
Inline6
Just in case you don't know, there are two "pre-filters" from K&N to cover the RE-0880.
The one Sky mentions is supposed to be an application for heavy dust exposures, and it supposedly restricts air-flow to the RE by ~10%. It kinda looks like a nylon stocking. (% of air-flow restriction numbers are from a K&N tech)
I have the 25-0880 which is a tight woven "foam" pre-filter that supposedly provides good overall protection at a loss of ~2% flow. This pre is by far the most used by TDR. This filter needs to be oiled lightly before installation. Best way to do this is use the K&N aerosol spray lightly on the surface of the filter, put in a gallon baggie... . less mess for your hands... . and "massage" it. Take it out of the bag and use a cotton bath towel to wipe down/squeeze out if it feels too slick. Remember, the RE comes pre-oiled and doesn't need oiling until it is serviced.
I have 13K on my K&N's with no off-road driving, except for a slow one mile trip on a gravel road in and out of my property. The RE looks just like it came out of the box when I peel back the pre and look at it. I think it will be a long time before I need to clean and re-oil the RE. I like this set-up.
As Sky says, Summit is a low cost source for these. The 25'r is about $20.