I have an old bike with an SRAM X0 9 speed rear mech. Yesterday the cage spring broke. It seems as though this spring is not available/user-replaceable (although the torsion spring is) so a new mech or mech cage will be needed.
The X0 has been the best derailleur I have used so I would like to continue with this system but replacement X0 9 speed derailleurs or cages no longer seem to be available. Could a 10 speed X0 derailleur be used instead? If the cage openings and jockey wheels were too narrow would it be possible to transfer the existing 9 speed jockey wheels and axles from the old mech to rectify this? Is the difference in movement between 9 and 10 speed just in the shifter or also in the derailleur geometry? If the movement is the same and the fittings are transferable I could fix things with a with a new X0 10 speed derailleur or cage. Otherwise it looks like a complete new (10 speed or more) gear set would be needed if I wanted to retain the same quality. This would also require new chain, chain rings and cassette: seems a lot to fix a broken spring.
Another option would be a different type of 9 speed rear mech and, if necessary, shifter. What is there that matches or comes close to the quality of the x0?
Any advice/suggestions