Ferdman is right, however It is difficult to view engine movement from the drivers seat, as well as standing in front of the engine. Another problem is in Australia the trade refer to the left side as Nearside and drivers side as Offside, as you drive/steer on the opposite side of the road, left and right and nearside offside are opposite. Now I've confused you and me!

If the shop has had a rough look, wait until they inspect thoroughly. The fact the mount is 12 months old does not preclude failure. Either have them inspect them thoroughly or check yourself, any signs of swelling/cracking or deterioration will indicate replacement if not actually broken. Regarding replacement, Phil at Fastlane, this site provider can sell you the parts, check this site. Re Gearbox, these are sturdy suckers and due to design of box and rear gearbox mount can withstand heaps, you won't damage it. The mount however is not designed for lateral front-rear movement to the same extent. If you have two broken engine mounts the gearbox/engine assembly can in extreme circumstances - ie emergency braking, move forward and damage the radiator. Besides that, it won't be a problem.

Manner of driving, oil contamination can cause a mount to fail, your best bet is examine and replace if necessary. If you intend keeping the vehicle for some time it is worth replacing as a pair, but thats my opinion, so be guided by what you find or the shop by inspection. Hope that helps.

Brian.
280SL