One year follow up on the base idea, with six months since last opened up and looked at. This is the thicker 2" polyester "Newfoam" batting material sewn down into the gutted stock airframe using black thread so you can see the sewing pattern. Batting was collapsed by the sewing from 2" to 1 1/2" and it looks like it settled another quarter inch or thereabouts due to air suction going through it (leaf blower effect).
Intent to this generation of trick was to come up with a Gunk engine cleaner washable (in the kitchen sink no less) very durable re-oilable air cleaner that has the characteristic high air flow & low air resistance of a high performance air filter while combining a very low initial cost, better than stock air particle filteration and a robust reliable/durable nature in the face of motor blowby fumes, sand, dust, etc.
This is the third evolvement of this cheapie filter idea and I do believe it is getting close to meeting all its goals.
This filter element has been in place for a solid six months run, so it has had time to get all dirty and gritty. Let's see what we got here.

Well, we've got a hell of a dirty mess -- my home town has lots of sand and dirt in the air and we've had a plenty of land clearing, road and other forms of bulldozer work to kick up plenty of dust and dirt that I had to dive through.
Note the free oil from the motor puke tube that has accumulated down inside the airbox -- this was about a half ounce of oil that I let out of the little stoppered drain tube after I took this picture. You need to remember to unstopper and drain this tube every time you drain your oil, BTW.
First question: Does Mazola spray oil (Pam like stuff) evaporate out to be all sticky and gummy-like and does it catch sand and grit and dust and HOLD on to it like nobody's business?

Yes, it is yellow, sticky and holds on to what hits it. These are full size grains of sand sticking to a smooth plastic surface because the oil won't let go once it gets hold of something.
The yellow spray on Mazola fry pan anti-stick oil seems to work as a filter conditioner oil just dandy, thank you very much. Does it really stick around on the polyester filter fibers though?

The oil is yellow and you can see it "sticking around" very clearly on both the top and bottom views, so I would say it does stick around and continue to do its job even after 6 months of sucking air through it.
Now, final and most important question: Did anything (no matter how fine) get past and through the filter batting & Mazola oil combination?

These top and bottom images are HUGE images that you can only see a corner of it here on the list without scrolling the scroll bar at the very bottom of the whole thread.
To answer this question completely for yourself, right click on the image, "save the image as" and save the full size picture over to your desktop then blow it up 800x with your favorite image editor and look 'till your hearts content. You can do the same thing on the dirty side picture and like me you will conclude that air borne dirt doesn't even get very deep into the dirty side before running into a gummy oil coated strand and getting captured and held. On the dirty side I can see down into the batting far enough to see clean white strands sitting there waiting for some dust to come see them.
Having torn apart the last one inch polyester batt version and finding that the finest dust didn't penetrate but a quarter of an inch, I think this slightly compressed 2" version has twice more fibers per inch and a good bit more depth in it to do an even more through job of stopping the finest dust and filth for an extended period.
Looks good to me, I put it right back into place UNTOUCHED to finish out a full year of use before looking at it again. It didn't need washing yet. I did not even add any more Mazola spray oil to it (it still had plenty of unused undirtied liquid yellow oil still trapped in the batting, easily visible from both sides of the batting)
Test continues .....

Oldfeller