Oil in air handler

You don't have a radiator either for antifreeze. So this is the long time air cooled motor. - Same as early beetles, early vans, station wagen, type 3's.

No, there is no spin on oil filter like American or other cars. They have a wire screen that is suppose to be cleaned(washed out in gas with a brush) every couple of oil changes. It is that ring of nuts underneath the car with the drain plug in the centre. Most everybody just drains the oil because the screen does not get clogged.

Bear with me as I try to compare things.
My 1973 superbeetle had an oval shaped "oil bath" air cleaner(that is a fibrous material is submerged a half inch in oil and the whole thing "which basically was a can inside a can and held together with clips or snap wires" was the air cleaner was mounted on top of the carburator. That was a stock factory set up. These units were just rinsed out in gasoline and clean motor oil was put in the bottom again. But they lasted like 50,000 miles before you would do.
The job. The principle behind it was. As the dirty outside air bubbled thru the oil, the oil would hang onto the dirt particles and the dirt particles sank to the bottom of the air cleaner.
It worked very well and probably contributed to the long life of the motor.
The 1972 VW van had a square dry paper filter, which fit inside a boxy plastic airbox. And needed changing with a new one when it needed to be done.
So, one has oil in it, which is perfectly normal. Which one do you have? Or maybe I should have asked. Have you ever changed the air cleaner before on this car?
If you have the oil type of air cleaner, split it apart and take the top half and put it in a tray large enough to lay it as it was sitting in the car and put some gas or other solvent(paint thinner) in there.. And swish the cleaner around to wash down the oil that is in the fibers and any dirt will come with it. With the bottom half poour out the oil that is on the bottom and wipe off the dirt that will have collected at the base. It will be as hard as clay. When you get all that major stuff out of the way then put in some of the solvent that the top half is sitting in and wash out the bottom with a brush. Yes I know it is messy. This is like once in a lifetime. After you done all that you can wipe out the bottom half with a paper towel and then put in some (1/2") clean 10/30 motor oil (or whatever your engine is using), slip the top of the aircleaner back on and clip it closed and then put it back ontop of the carburator and tighten the collar screw. You have cleaned the air cleaner. ( Do not use soap and water in this operation)
There is no pvc valve. Honestly, you must ask people who drive VW's for any information. NOBODY else knows. It is a different car that alot of mechanics won't touch.

As there were nothing to change (air cleaner, oil filter) the shops could not make any money on part sales either.
The gas filter is an add on somebody else did(for VW does have a wire screen for the fuel at the fuel pump.-Washable/reuseable.

Hopefully, the air cleaner was dirty and this was your problem.

Other than that, you have accumulated 160,000 K on this car and it is getting tired. The best you can do for it is find a person who knows VW's to give you an assessment as to what can be done. I tend to steer away from dealerships cause all they want to do is sell cars.
Talk to other VW drivers when you see one drive by.
Remember.
The friendliest people in the world drive volkswagens.