I bought some black "liquid electrical tape" that is supposed to work, but haven't tried it yet. I need to clear out a space in the garage since apparently it causes some bad fumes.
The bellows I'm going to work on have lots of pinholes, but no big rips or larger holes.
Please let us know how it goes.
If you take a piece of 5x7 photo paper and trim off 1-1/4" ( to make it 3.75x7 inches ) it will fit perfectly in your 3A and it can be a lot of fun. The "postcard" format makes nice sized contact prints.
A lot more fussy, I also trim just over 1/4" from 4x5 film. I made a "film holder" from black construction paper that fits perfectly in the back and holds one of these. I wish I'd just bought 5x7 film and then I could have used it like I do with paper negatives. If anyone has boxes of ADOX CHS 25 ( Efke 25 ) in 5x7 and would like to trade for frozen since bought new boxes of 4x5, I'd be willing to trade and pay a "difference"
I hope you have fun with your 3A!