Alain,
Merci pour la réponse. Peut-être le vernis à ongles suffirait-il. Pour ce qui est de l'encre de chine, je crains qu'elle ne supporte pas l'enroulement/déroulement des rideaux. Il faudrait un matériau suffisemment souple (silcone ?) pour cela.
Décidément, ces lectures vespérales s'avèrent fructueuses et je crois avoir trouvé réponse à ma question. Je vous poste quand même une copie de la précieuse info, au cas où d'autres personnes connaîtraient le même problème :
DIY hole repair
Alternatively, if it is only a very tiny little hole, then the following tip by George Lottermoser <imagist@ concentric.net> is worth a try:
[To patch the hole in a Leica cloth shutter,…] A teeny tiny bit of the liquid black rubber compound they sell for tool handles at the hardware store, judiciously applied with a que tip or tooth pick, to each side of the shutter; did it for me. Still going strong after 3 years.
In Feb 2002, Anon Terry <anonht@ yahoo.com> added:
BTW don't be squeamish about such a "low-tech" repair. The shutter on my M6 has had an 8 year old's finger poked into it, and two Shoe Goo repairs [to plug sunburnt holes], since I bought it 4 years ago. No servicing, and works great to this day (and I still refuse to use lens caps). The secret to a successful Shoe Goo repair is to spread it thinly and evenly, using the flat end of the toothpick to gently smooth it into the shutter fabric surrounding the hole on the front and back, and leaving the camera with bottom plate off to dry overnight before firing the shutter again.
Along with tool-handle compound and "Shoe Goo", you can also use Kodak Black Liquid Opaque or Liquid Electrical Tape. All of these are basically black rubber liquids which set to give a light-proof, flexible rubber film. Just make sure you don't get carried away and use too much, or else get impatient and fire the shutter before the liquid has properly cured!
One thing you should keep in mind is if you do an obviously crude or sloppy job, then even if the repair worked, you can kiss goodbye to at least $300 of the camera's value should you wish to sell or trade it in at a later time.
Merci à Anderw Nemeth pour tout ça. Alain, si tu veux quelque chose de plus durable pour l'appareil de ton grand-père, ce message est pour toi...