Mamiya foam replacement (set of 2 foams for each 1 bid) to prevent light leak made for the RB revolving adapters (both sides), will fit all 3 types of RB revolving adapters (RB, RB PRO-S, RB PRO-SD).  These sponge foams are original Mamiya made in Japan spare parts, same ones they put on brand new revolving adapters and the same ones they use at Mamiya service stations in Japan for replacement. 

If the light foams on your revolving adapters is old, falling apart, becomes gooey, then this is the original foams to replace with, already pre-cut form and just use slight dabs of glue along the foam gap (on the revolving adapter) then tuck this foam on gently.  (remove all old foams and gently scrape off residue first).

(this listing is for the FOAM only, the revolving adapter on 2nd and 3rd pic is for reference only as illustration)