The wheel balance , even a tiny bit can be a bit vibation problem. Maybe a belt even broke in the tire, but mosr likey the tire just needs balanced, and you said you wanted the cheap fix to sell the car, balance the tire for $15 and see if it is the issue. Spinning the wheel or the rotor or the hub with the car up and the tire on or off is a hard way to test. THe unsrpung weight of suspension, no load on the bearings, the rotor not being lined up due to the one set screw, the brakes dragging, etc all give false readings. Good luck
I would balance the tire at a very high quality shop, preferably one that can balance the tire on a high speed machine that does it under a load, like a Hunter machine.
IF it is not the balance you are not out much and you can look at the brake rotor or the pads. Check your brake fluid level too.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red