I finally bought two A12 backs for my Hasselblad 500cm and I now have a whole kit. One of the backs is a newer one with an ER serial number but the other one is an older 80's model that I bought for real cheap and it has 3 holes on the back of it which is, of course, letting light in. It's missing the plastic ASA dial, I guess, and it looks like there were once three rivets that held it in place. Anyways, anyone have any ideas on how I can plug up the holes? In the short-term I was going to tape it up but I am unsure what kind of tape will completely seal out all of the light. Thanks in advance.