Both handles on Bob Goodrich's SRR-13A had stripped gears. Close inspection revealed the stamped identification "Boston G-171". An email to Boston Gears revealed that the G-171 spur gear is still manufactured and can be ordered through your local friendly Boston Gear dealer. The gears aren't exactly cheap at $12.91 each plus shipping from the local Boston Gear representative. The fact that the same gear is still available after 50 years is a miracle.
The center shaft for the gear is staked, and made of steel. Bob drilled a hole about 3/8" deep in the shaft with a #43 drill bit and tapped the hole with a 4-40 thread. The new gear was installed with a 4-40 screw.