Mamiya RB Back Insert Seals
USCamera custom 6 piece light seal kit for the Mamiya RB 67 Pro / Pro S 120, 220 and 645 film-back inserts only. This 1/2 of what I recommend you replace. The other 1/2 is the shell kit. The RB film back consists of the shell and insert. In checking film backs for years, if the shell seals are bad so are the insert seals, for that reason, I recommend replacing them as a set. You may purchase the complete film back kit here. The insert kit includes door channel seals on the back of the top and bottom covers, top/bottom seals left guide roller plate and top/bottom seals right guide roller plate.
Make sure to check out the placement guide for the RB Pro and Pro S film back insert, and shell here.