My 89 300TE recently started to hum/vibrate around 45 mph while accelerating or going up hills. It seems to get worse as speed/throttle increases and it happens in any gear. There is no/low vibration while coasting. The vibration has been slowly getting worse over the last few months. I occasionally use it to tow a utility trailer (approx 2000lbs) and it was particularly noticeable when taking the trailer to the dump today - haven't towed anything in about 12 months.

The car has about 230k miles on it, and I've put about 90k of them on it. I have never replaced the flex disks.

I read LarryBible's thread about doing some research before throwing parts at driveline vibration problems, also the part about altering the seat of the U-Joint looks like a good thing to try before dropping the exhaust and throwing flex disks and a center support bearing at it. But Duke mentioned that the flex disk should be replaced at 60k or else bad things happen so I'm wondering if I should just replace them regardless. While I'm in there should I replace the center support bearing? The car had an oil leak at the headgasket (which was repaired about a year ago) but this resulted in the undercarriage getting persistently coated in oil. Can that ruin a flex disk?

About the tires - they're about 12 months old and the MB dealer performed the last wheel alignment. Does this type of vibration seem like a tire problem? Should I rotate the wheels or swap them with my other 300E?

Thanks!

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89 300te 222,222
92 300e 190,000