Not so retro, but I was given a Magura Asgard fork by a cycling friend... He'd bought it new, shipped in from Europe at some expense. Being a roadie new to MTB, he locked out the fork and began climbing the access road to his chosen trail. As he began singletracking, he neglected to open the lockout. A few big hits later, and the compression damper/locout blew out.
I tore them down and found the lockout lower seal had been blown out of the leg. The leg had fractured at the circlip groove, liberating its guts. Both legs are the same (with different internals), so I decided to use a lathe to face off the broken end, cut a new circlip groove 4mm above the old, and move the counterbore up 4mm as well, on each leg. Then re-assemble...
The lathe work went easily enough using my step-father's machine. Took about 10 minutes to set up each leg in the 4 jaw and steady rest... A few more minutes to fix up a cutter to cut the correct profile for the circlip groove, and off I went. Pretty simple, even though I'd not operated a lathe since 1994...
To prevent the fork from being blown up again, I largely disabled the lockout by drilling a pair of very small holes in the lockout valve plate, so it's never truly closed, just slowed. Lockouts - who needs'em.
That done, I reassembled the forks last night... A few times actually, as on initial assembly, the rebound adjuster leaked oil. A fresh Oring sorted it. Now the fork has 88mm of travel instead of the original 100mm, but that's hardly an issue. Most of the loss is in the rubber bottom-out bumper I added, because I think suspension should always have bottom-out protection.
Finally, installed on my wife's '97 Hardrock AX (in place of the crap Judy J1 pogostick, saving 1.5 pounds, gaining 18mm travel and.... Hydraulic damping). The rain abated this afternoon, and she reports that the only word she could come up with to describe the fork's action was "Plush!".
A fun puzzle.
J