I have a 1984 380 SE it sat for 2 years on new rubber(Remington Premier Something or other SBR's )I have a vibration at about 70 or so also. The tires were brand new 2 years ago and not driven at all, maybe from the tire shop home. I know tires flat spot if they set for an extended length of time(radials or not). I do not know if the flat spots ever recover.
I suspect that the tires need to be balanced and rotated and will attend to that tomorrow. I feel the Vibration in the steering wheel, but not the Shifter(because it's not connected to the tranny directly.) Vibration is transferring to the car body as my rear view mirror is toast(sun baked and the actuator broken out)vibrates a lot also.
I also know that the spare Mag wheel is bent per PO. Now i wonder if any or all the other four are bent too.

Any suggestions?

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.