I have the new gears for those transmissions to go back stock or convert to the later 1940-up. It sounds like a new synchronizer might solve most of the problems. As a rule the 1937-39 gears can be purchased new a little cheaper than the later ones.
The original 1937-39 transmission had straight cut gears on the reverse idler gear, the sliding low/reverse gear and the 15 tooth center gear on the counter shaft gear. These gears were bevel cut on the later 1940-54 transmissions
