I dont think they will fail suddendly and cause harm. Is more a subtle decline.

In my expirience the vib should be less as rpm is increased (if you wanna talk vib's, feel a diesel with a bad mount).

You might also want to take a look at trans mount and flex disks. Flex disk would be a prob if it failed during use.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)