This collection of ZF repair lore is priceless- thanks, Rocky. It seems that the main variables are part of the design. We are dealing with thousandths of an inch combined with metallurgy in high torque transmissions. In trying to save the expensive precision gears while replacing the all-steel synchro parts that wear faster, experience from WW-2 apply. Gear-steel just doesn't weld well. Some of the elements in gear-steel change phase or boil off at welding heat. It also doesn't plate well. I tried welding gear steels with a TIG and failed miserably. So easy backyard fixes were doomed.
Combine that with the fact that ZF gear-steel is 'different' from 8620, 9310 or common Ford gear-steel. Ford found that out in 1970 when, after complaining semi-publically, their own testing found that ZF's steel was 'better' than Ford's. Dunno if it was tougher, stronger, better-wearing or all the above but compared to a Ford Top-Loader or a Muncie, a ZF was 'better'. Is part of it the heat-treat? I know D Quella spent years working on transmission gears and synchros, not just for ZFs but Indy-car trannys etc. Glad to hear from Ron that he succeeded.
ZF as a company was founded in Germany by Count Zeppelin to make parts for his airships back in the1900s. Because at the time, he couldn't find any that were good enough. ZF later got into parts for vehicles, ships, submarines and other prime movers. Over the past 120+ years (plus two major wars for motivation), they obviously learned a bit about steel!