I just rebuilt my '37 gear box for the same reason. I found in the 29-49 parts manual a bushing listed for these boxes that helped with chattering or sticking. If you pull it apart it should have a 2" long steel spacer behind the sector shaft seal. It does nothing, I really don't know why its in there. The replacement bushing goes in place of this steel spacer to help support the sector out on the end. I replaced the other two bushings and added the third one. The small bushing in the cap is a odd size no longer made. I had to buy a oversized one and have it turned down to fit. The others are standard sized. I used a hand heald die grinder with paper sanding roll to custom fit the long bushing. I was really an easy job. Mine is just now starting to free up a little. It was pretty tight when I started, but I figured that was better than being loose.

I bought the bushings and seals from my local bearing supplier for less than $10.

Seal #11055 Chicago Rawhide (NAPA)
2" bushing #CB-1820-16
1 3/4" bushing #CB-1820-12

Joe