Can this gearbox mainshaft be salvaged?

A spacer ring broke and the remaining bits did some chewing on some spines. I was thinking it might be worth welding/grinding/machining the ends of the splines. A steel spacer ring rides on the end of these, so I'd assume they need to be straight and clean to avoid the same issue happening again.

BTW, this is a TR6 A-type overdrive mainshaft. A "new" aftermarket part is available for around $275, but I'm not certain of the quality. This shaft is in good shape otherwise.

Maybe the topic question should be "is it worth rebuilding yet another TR6 gearbox when a Toyota 5-speed swap kit exists?"

I imagine a competent welder with a TIG setup and some hardfacing rod could fix it, possibly without heat treatment.

Also, do you have a assembly diagram or something to that effect to show what these splines do? Are you sure the face of those splines are critical? If its just acting as a very low load thrust surface for a spinning spacer, and that's the worst of the damage, you could probably clean it up with a stone and call it good.

How many times have you been into the transmission lately? Is it a street car or any sanctioning body rules you have to deal with? The ODs are kinda cool when things are working - giving you a 7-speed. OTOH, what other transmission options are out there beyond the $$$toyota conversion kits? The GRMer in me wonders what it would take for a miata transmission or others that are junkyard cheap. Probably fix for above is welded, machined and don't forget to re-harden/heat treat.

This is in an autocross TR6 that isn't used for any sanctioned group, just for fun. We're way past that since it's running EFI with Megasquirt. The power output is around 160+ at the crank. The previous gearbox had been in the car for several years was replaced with one rebuilt (by me) simply because a rebuilt engine was going in. The new one lasted less than 1000 miles. The spacer that broke was used and may have been weakened. I also believe the overdrive engagement was a little too brisk and may have helped the breakage along. Overall, one broken gearbox in 14 years isn't too bad.

I'm not aware of swap options other than the Toyota conversion. Parts are really starting to dry up/get expensive for rebuilding Triumph gearboxes, though. We have lots of spare gearsets, just not many A-type mainshafts. I'd like to try doing the welding/machining myself, but I only have a MIG welder. It's more than possible doing this myself could lead to another quick failure.

The new aftermarket mainshaft may be OK and overall cheaper than another failure where steel ends up in the oil. We could probably find a good, used mainshaft as well. I just hate to throw away an increasingly rare part if it can be repaired.