Fortunately, the roll-pin parts remained in place (two in the gear and one on the shaft) but unfortunately the gear teeth have been damaged), so I’ll have to replace it. Also, the legs of the shaft stop had broken (I think I’ve located those parts too), but I’m not sure if the two failures are connected - ie. shaft-stop failure caused or contributed to failure of the roll-pin, or vice-versa.
Incidentally, do you know if the roll-pins (gear and clutch-dog) are metric or imperial ? My measurements suggest imperial - 3/16”, but I wondered if they might be 5mm … ?
It did cross my mind to replace the gear roll-pin with a spiral type pin to increase durability, so it’s good to know it’s a tried and tested modification.