Given the number of motors out there, it would be helpful to figure out how hard this might be, how expensive, and whether you need special tools, etc. I guess someone should be selling the gears, in the US?
The gears in my Mac are available and are composite, supposed to last longer. They say you need a gear puller, but the cover looks simple. I guess (pure guess) the Bafangs might start to need replacements at 2k and up. I'm hoping for 5k.
Hope it turns out to be simple and cheap. Be good to know if the 48 volts will be a problem, as well...