When I got my Rb I read about the seals being bad on those cameras. They mentioned foam and felt. I dug out the old foam and went down to Wal-mart and bought some felt. I comes in a 12 in. X 12 in. square or there abouts. I cut it with a hair cutting scissors and glued it in with rubber cement. It has worked great and I haven't seen any light leaks. I repaired another one that way but haven't tried it out yet. If the door doesn't close, I just pulled out some and replaced it until it did. You can buy those expensive foams seals but they will eventually turn to gum where as the felt won't. I haven't heard any reason not to use it, so if it isn't a good idea, stay with the foam. Ric.
I've used a thin adhesive-backed felt, too. It's worked well on some 35mm SLR backs. I think the foam kits are over-priced and often overkill.