My rear shock (Monarch 3.3) has decided not to hold any air any more.

They are £99 on CRC at the moment but I guess they can also be rebuilt. The shock is less than 2 years old. Is it worth rebuilding and roughly what would it cost?

Can it be upgraded or enhanced so it lasts more than 2 years?

A proper service would probably cost you £60+ and you would still have a 2 year old shock. I’d buy a couple of cheap ones now if you plan to keep the frame.

rebuild the old one yourself, if it goes wrong buy the new one

If you buy the one off CRC just make sure it’s the right tune, if it’s not you might have to send it off to loco for this to be changed