I looked into this quite a while back (maybe mid 70's) and found that some manual transmissions had the cluster gear on the top and some transmissions had it on the bottom. If the engine was not running, the upper shaft was turning inside the shift rings and the lower gear was not turning at all. The lower gear was not moving any lubricant up to the upper gears unless the engine was running. If this were towed very far, the lubricant would not be replenished in the bushings and they would fail within hours.
If you look at an early VW Beetle transaxle, the input shaft is on the top and the output shaft is on the bottom going to the pinion gear. The 3-4 shift ring is on the top shaft, while the 1-2 shift ring is on the bottom shaft. When the car is being towed, the 1 and 2 gears are not turning but the shift ring is in the lubricant. The 3 and 4 gears are turning and bringing lubricant up to the shift ring. Everything is lubricated and should last a long time being towed. > I was under the impression this was only an issue with automatic > transmissions, which have an oil pump driven by the input shaft to > lubricate some of the moving parts. As far as I know, that's not > true of any manual transmissions, but I'm far from being an expert...
