I have been working on the body of my 122 and trying to get it ready to paint. Got all the trim and bumpers off except the front and rear windshields and this little piece of trim between the rear windshield and the rear door.

How do I remove or should I not?

When I was removing trim from a junker a few years back, I removed that particular piece by unbolting it from inside of car (I seem to recall going in through the trunk opening)

Even with the tiny bolt loosened, the trim piece stuck to the metal of the car (maybe held on by putty?) I then used a plastic spatula to remove; a credit card probably would have also worked.

The trim strip is held in place with 2 bolts, that have a square head, fitting into the inside trim rail. You can see the 2 holes on the following image. I think I had to remove one nut from the trunk and the other after the back seat was removed from inside the interior. I do recall it was very tight and yes, likely there was some gray putty to help seal and protect the joint.