I had the gearbox mount break in my Mk2 Citroen Saxo (one of three mounts holding the engine, gearbox etc up). The engine fell down due to the lack of mount, and the gearbox hit the floor (and cracked).
I will, of course, be replacing the gearbox and the gearbox mount, but should I replace the other engine mounts? I am concerned about the stress that may have been placed on them.
In the same way that you don't technically "need" to replace tyres or shock absorbers in pairs, I would suggest it best practice to replace the other mounts. If one has worn to the point of failure, it will be presumably the same age as the others. Plus the rather dramatic failure plus the extra stress placed on the other mounts leading up to the failure, the other mounts in the car are likely to not be in the best state.
You could, if your goal was to simply make the car drive again for the lowest possible cost, replace just the failed mount. However, if it were mine, I'd replace the others at the same time or as soon as affordable to do so as a sensible precaution.
You don't NEED to, but be aware that the other mounts tend to wear more quickly after 1 has been replaced. If you don't replace the others, keep an eye on them.
