By the way, I got two Ibsor shutters running again after a quick simple fix last week. You open the shutter from the back, by unscrewing the four screws. Remember where the shutter blades should go (they are numbered). Small drops of naptha on the speed gear axles, and then tiny amount of fine oil, was enough for my Ibsors.
Ibsors are simpler and cheaper than Compurs, but not bad. B and T are on the same wheel as the speeds, and there's no need to cock the shutter, making it fast to work with.