I have a brass desanco fitting into a cast iron stub-out.
An ABS elbow fits into the desanco with a nut and flange on the other end.
The brass desanco cap has a crushed seal (part of the cap) with a hole in it.
The plastic elbow will not move; its stuck.
Are these glued in place or what keeps it rigid?
No way to remove and replace the cap.
Should I try silicone rubber in the cap?
or should I cut off the elbow and try to remove the remaining ABS so it can be replaced?
or should I cut off the elbow and use a Fernco coupling?

Here are some photos:

In the mirror, you can see a hole in the seal/washer.

Name:  DSC01825.jpg
Views: 483
Size:  71.3 KBName:  DSC01828.jpg
Views: 404
Size:  51.0 KBName:  DSC01830.jpg
Views: 384
Size:  54.0 KB