Is it worth a five-minute investigation to determine if the skinny bit at the top (I think it works out as 5mm from dimensions given) could be made bigger? If you poke a 5mm drill into the hole, it should clear. What of a 5.5mm or 6mm? Sometimes the manufacturer's made parts generously-sized for ease of assembly or speed of production whereas an artisan-fettled item can be made to tighter specs.
A lot of the cause of the bending is the use of a nut (and hence a spanner) to lock it. It is like a split cotter; it needs minimal force as the clamping action is greatly magnified by the pitch of the thread (work out how much angular rotation of the nut is needed to get one thou' movement of the clamp). So on the new one, maybe dispense with the nut and make a dedicated locking handle with no more than a 1 1/2" long stem on it.
Yes Argo I agree wholeheartedly with your assessment. Especially the fact that the nut is one of the causes of the bending. I agree with the idea of making a handle that will limit the torque that can be applied.
I think when Harrison designed the lock they assumed that users would be imbued with a modicum of engineering "feel" and would tighten it sympathetically. Clearly that has not been the case throughout the life of the machine.
I'm going to be looking to see if there is scope for the dimensions to be subtly increased to make the part stronger, too.
Thanks for a very useful and thought provoking post.