Broken Hasselblad A12 back question

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.

Try black electrical tape.

I have an early "peep hole" 12 back where the entire hinged asa reminder that covers the peep hole is missing.
I made a piece if cardboard that fits and keep it in place with gaffers tape. No leaks in 7-8 years.

Your issue sounds like the holes are way smaller (although I can't see them in my mind this early ) than in my case so I'd image tape will work fine.

Also, if there is something internally wrong with the back could it harm the camera body? I'm wondering if its even worth the trouble.