I've had no luck so far still trying to figure out a replacement piece of rubber.
Meanwhile I have scanned in the programming reference I received with the player for the Model Three upgrade. There appears to not be another copy available online digitally, just for the Model Two, so this should be helpful to a few people. Please note that while I removed the original staples and the pages were still tight, pages 89 to 101 are missing.
https://www.dropbox.com/s/sjexocs6al...duced.pdf?dl=0
Edited: Actually, if anyone wants to look at ANY of the available service documentation I have on hand, I just uploaded it all to archive.org. It should come up in the texts section of you search "Discovision".