I agree with all of the above. When I found that I was having to work on the original starter (on my TR3A) almost every year and it twice quit during long drives (each 2000+ miles round trip); I bought a gear-drive from TRF. Their ad said it was new, but what I got had a "rebuilt" sticker on it. Works great, although after nearly 10 years of daily driving (not counting the few years it was idle after the wreck), I think it may be ready for "freshening" again.
As a side comment, I changed the wiring a bit from the usual recommendation, so that the original solenoid only switches power to the new solenoid on the starter. That way the motor current doesn't have to pass through the original solenoid (which had previously lost some of its smoke), but the starter pushbutton (on a TR3) doesn't have to handle the increased current (and kickback) of the new solenoid, and I got to keep the function of the starter button under the hood.
The change was easy, I just moved the battery cable to the bottom original solenoid terminal (where the heavy wire to the starter motor goes) and ran a new wire from the top terminal to the solenoid on the starter.