I can repair most sextants. I have many replacement mirrors in stock and can get almost any mirror duplicated at a local company.
The most common repair needed on a sextant is cleaning, and oiling. It is essential to clean and oil your sextant after every ocean voyage. The salt moisture will accumulate in layers on the sextant over time, hindering it's functionality. Multiple layers of accumulation can be more difficult to clean. The best cure is always prevention, and it only takes a few minutes. Cleaning your sextant after every sea voyage is a simple matter of putting it under hot running water to rinse off the salt moisture that has accumulated.
I've seen so many times, that upon the preperations for the next voyage, maybe a few years later, the mariner takes out the sextant and discovers that it is all green and the mirrors have de-silvered. Consider this, if it is okay for the sextant to get damp with sea air laden with salt, it is likewise okay to wash the sextant under clean hot water to remove the salt. Throughly dry the sextant and then apply light sextant oil to all moving parts before storing it in a clean dry place.
The second most common repair is simply adjusting the mirrors. This is not a difficult process, but it takes training and careful handling. A sextant becomes out of adjustment with normal handling and temprature changes. The sextant can also be easily knocked way out of adjustment by dropping, or otherwise roughly handling the sextant.
I can adjust your sextant to remove all error and teach you how to do this yourself. It is not usually necessary to allow for IE (Instrument Error) when doing the math on your sights if you know how to calibrate your own sextant and check it daily before shooting an object.
I have many other new and used sextant parts and scopes in stock. If I don't have the part you need, I can usually locate it for you.