To my experience, there are only two ways to have a bad engine mount:
- Some oil is reaching the mount and the rubber slowly disolves until the inner shaft is loose
- A manufacturing defect
The mounts are only a piece of rubber with an external and internal steel section. It is glue to both parts. Nothing can wear as it is not a moving part. The rubber is compressed with the forces.
Usually any other part will break (transmission, engine, driveshaft) before a mount.
If you look at the engine running at idle, and compare with a v8, you will see that a 3 cylinder does vibrate alot and stresses more the mount. This will eventually show if a manufacturing defect is present in a mount
By the way, I beleive that there are 3 engine mounts. But I am not sure
Addition:
I looked at them on my car. They are Very big. There is No Way I would pay for them without having the original piece back. To inspect it in case they charge for nothing.