Last thing i'm fuzzy on is air filters, some clean with oil, some are dry??
If you have a paper filter, it's dry.
If you have a foam filter, use filter oil. The idea is that dust and stuff will stick to the oil. Don't use too much oil, just enough to make the whole thing sticky. It's a messy job, I found the best method was to put the foam filter in a plastic bag and then add oil slowly, rubbing it into the filter inside the bag to keep your hands clean.
Before fitting the filter, apply a bit of grease to the part where the filter touches the body, and don't overtighten, as that will bend the filter away from the body, leaving a gap for dirty air to come through.
You will still get your hands dirty and full of oil, but the plastic bag method works, and is very economical on foam filter oil, which is quite expensive.
It takes a bit of trial and error, unless you can get someone to show you.