mm, great question. I hope someone has an answer. My car is 11 years old, and all the seals are still soft. Then again, since year 8 I've conditioned them with 303 UV protectant. As far as bushings, not sure. Most of mine were replaced at 70k/7 years due to squeaking. If you're past a decade, I would say that you need to look at them. That said, my motor mounts are original and show no signs of failing

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL