Vice.That stain is actually overspray of the glue the factory used when fitting the headlining. It's on the underside of the headliner and therefore doesn't clean off. As the glue ages it yellows.
If you're thinking of vinyl spraying a headliner there are two things to consider. One is if the headliner is perforated, paint will fill some of the perforations depending on how thick the paint goes on. Vinyl dyes are thick so you'll have some areas that will look non perforated or smooth. Number two is if the headliner is 'Black dot' material where the dots in the headliner are actually printed onto the vinyl. Paint that and you have the same problem as issue number one.
If the headliner is nice, enjoy the patina. It's just a symptom of an old VW.
If you want a nice gentle cleaner to clean any part of your interior, try this
http://www.doubledauto.com.au/vinyl-cleaner/
You will clean any dirt on your headliner with it and it's great for your seats and door cards. If you've got a black dot headliner just try a section first.
Cheers
Brad
Ha! Beat me to it Rod