I know K&N makes a special oil for this, but is there any substitute I can use?

 

to be on the safe side i would stick to what K&N recommends otherwise the stuff you could be using could damage the material of the filter.

 

I read somewher that K&N oil is mineral oil mixed with red dye.
The cleaner is just laundry detergeant and water!

 

The reason behind my question is that I'm taking out and using my RU3130,which has been in storage for a few months. It still has a purplish color to it(not too dirty), but it does look a bit dry. Can the oil evaporate like that? I wrapped it in a plastic bag before storing it.

 

no it should be fine! If its still has that red colour on the filter and not white or brownish tint on the majority of the filter then it should be good!

 

it's only about $10-15 anyways for the proper k&n cleaner and oil. not bad if you ask me. just make sure you don't over-oil the filter! i did, and it was drippy and left small drip marks eveywhere i parked for two days.

 

You can try ATF, even cheaper for a whole quart.