Duncan,
Recently i came accross this article on a new tune up service, and the seem to offer you the option to send in your bits to be tuned up. From what I can gather you dont need to send the whole mount just the gears etc.
http://www.andysshotglass.com/astromo_mod_store.html
Edit: on reading further again now, it looks like they have discontinued the gears only service.
But i recal a post from some time ago mentioning a tune up service here in Australia by one of the local retailers. I will try and search for it and see what i can dig up.
Regards
Fahim