It should be as easy as looking at the filter to tell if it’s pre-oiled, it will be a reddish colour from the dye in the oil.
I grew up out past Dubbo and I and many people I knew always had an insect screen to protect our radiators during times of locust plagues and an OTRCAI is no different as you can’t afford to block the flow.
Normal insect contamination should not be a worry as long as you clean down when you see any signs of a build-up.
My K&N’s says to clean and oil every 5,000k as a guide and more often and as needed in dusty or dirty environments which could mean a daily inspection or clean if it's a really bad location.
K&N’s are not necessarily the best option if where you live is very dusty.
Reusable filters are not maintenance free, in fact they are the opposite and require regular inspection, attention and cleaning and that’s one reason a lot of people still prefer to use paper filters.
Always make sure you have a recharge kit or something similar on hand.