Hi Jusbay,
Try this method. Find a black umbrella that has a broken spine or broken ribs, in order words, you will be too embarrassed to bring it outdoors. Cut a portion of the black fabric out and then cut out 2 small square pieces of the same size, likely about triple the size of the hole on your shutter curtain. Next, get a hot glue gun and glue the 2 pieces of cloth on both sides of the leak. Apply the glue on a piece of board first and using a matchstick or something small, apply a bit of the hot glue on the 2 small square pieces of the fabric, after which you then stick them on the curtain. Make sure they stay flat and smooth. Leave it overnight. Do not apply the hot glue directly on the curtain.
1. The black umbrella fabric is very thin and smooth which make travelling in the shutter chamber obstruction free and idea for this DIY repair. It also has a greater degree of opacity. especially you are using 2 pieces, 1 on each side.
2. Do not use superglue as it becomes brittle when dried.
3. Do not use electrical duct tape as it peels off within a short period of time.
Of course changing the whole curtain is the best method but its not economically feasible for a Zorki, Zenit or Fed.