Garry,
I agree. I think there would be a large market for the spares--primarily the synchronizers, some castings and the gears. Many of the other smaller parts like studs, bearings, seals, etc are standard DIN items and can be readily sourced. I know that some of the parts require specialty machining, particularly the ones on the main shaft, but I've got to believe that manufacturing and machining technologies have come a very, very long way since these boxes were first manufactured and the costs to make these "intricate" parts have got to be less than what they were 45 years ago. I still can't figure out from their website what spares are currently available. An inquiry I made some time ago went unanswered. I'm not in any dire need of parts now, but I can see the day when I might need something and would like to know it is available. I'm really glad I had my box rebuilt back in 1983 when I was stationed in Germany. I was having some leakage back then along with some synchronizer issues. The ZF factory was set up to rebuild these back then and I'm confident the job was done right, but that was almost 30 years ago now!
George Desiderio