While refurbishing the paper tower for my Monotype caster I found that one of the pivot pins (part 16G, on which the locking pawl pivots) was slightly bent, and was nearly impossible to straighten properly. The bend was hard to see except when the pin was installed, and the pin was too short to tell exactly where it was bent.
Rather than trying to fix the existing pin I made a replacement one.
The geometry was fairly simple, but the dimensions had to be accurate to ensure that the pawl did not have too much play, which would have led to increased wear of the ratchet wheel and misalignment of the ribbon holes over the air ports. It fits well, although I cut the threads a bit deep, possibly weakening the threaded portion of the pin, but I don’t think there is enough pullout force to break it.
The paper tower is now reassembled, except for the two lower covers, and has been reinstalled on my caster. To discourage future air leakage around the base of the tower I applied a thin coat of spray adhesive to the mating surfaces. I actually sprayed it onto a piece of release paper, then applied that to the area around the ports, so that over spray would not enter the actual air lines. The adhesive should be strong enough to resist the air pressure but still weak enough not to prevent future removal of the tower. I would have used brush-on gasket sealant if I had had any.
The next job is to adjust all the linkages.
I saw something hinting that this post is actually slightly eccentric. This would provide a means to adjust the idle position of the sprocket pins so that the punched holes in the controller ribbon are positioned directly over the holes in the girt when the ribbon stops in each cycle.
I have no definitive proof of this, though. The post I removed from my caster did not appear to be eccentric.