Used a cut square of vacuum cleaner hepa filter for underneath the screen that snugs down also under the stock air filter. Should wok as designed now.
Stock there was a piece of foam there under the airbox to sit in that location. The foam in my airbox was completely crumbled, which is no surprise, it being 37 years old. I used a couple of scraps of microfiber as my impression was that foam was chosen to filter, and also to soak up the oil that gets shot up there from the crankcase -- the hepa filter media will work just fine as well. The main reason I put in the effort was because without anything in there, the oil was shooting up and dirtying the bottom of the air filter.
Note that if your setup is still like stock, there is a rubber hose coming down from the airbox in that breather assembly, that has a rubber end that you can pinch to empty out any other accumulated crap and oil. You may want to check it to prevent any additional red herring oil drips.
