New owner , what’s this piece called ?

the vertical plastic trim that’s at the back edge of the rear door on the passenger side, what would be considered the c pillar.  The one I’m buying is missing this piece and I can’t seem to find it online - probably because “missing damn piece of plastic “ doesn’t yield many results….

That piece is called the "fly away panel". That piece is missing is a common problem. It flies off when you're driving and by the time your realize it, you're miles down the road.

There not impossible to find, but awful close. You'll need to be very vigilant in your search for another one.

Tom

Next thing. Are they specific to the OCC or will a road master or caprice version work? And are they wagon only…. Wondering if I can broaden my search …

Wagon only. Caprice did not have them. Only the 1991 Olds had them. All of the Buick wagons had them.

So a Buick wagon or 91 olds wagon would be a suitable source, correct?

Correct

Thanks for your help guys. I cant wait to get this car in my possession and get started enjoying it. I've been wanting a wagon for a long long time and although the circumstances suck (buying from a family friends widow after the husband died last week), it will be good for me to keep the car and enjoy it as much as he did.