[SAJ]

Nkaminar, did you by any chance photograph your modern drive before you put it in? I would like to get one like you have, but do not see such available anywhere.
I have broken the slotted collar on the end of a standard bendix, which is why I changed our cars to barrel drives.
Re-cutting a new woodruff slot and drilling a new retaining screw hole 3/16 closer to the starter might be a solution for the Weldon with beefier helix teeth, but the fine-toothed Indian ones are too brittle for my liking. On both types the rubber end buffer mechanism jammed immovably inside the metal housing so the retaining screw could not be undone. A positive stop against the starter end plate rather than internally inside the drive might prevent this too.
The only springs inside my drives were the tiny ones providing friction on the helixes.
SAJ in NZ