I haven't mentioned this because 201/202/124 cars in general don't have control arm problems. BUT, they can be created.
If this is the case I can tell you about one similar just this week. Best of customers brings in her 91 420SEL to wait while we balance out a shake at 55. My best tech balanced and rotated the low mileage Michelins and didn't do squat to the problem. I drove the car and sure enough at times it would about take the steering wheel from ones hand. The vibration went away after 65mph. Sometimes if one was accelerating no vibration woud occur. Sometimes a small turn at speed would creat the vibration sometimes it would remove the vibration.
I placed the car on the lift and viewed the suspension. Everything was good including the rear suspension ball joint (front lower control arm rear ball joint/mount). This joint was not only good looking it was practically new. Knowing that we are the only people who have serviced this car for at least ten years, I know we must have put the mounts in. This doesn't stop me from condemning them and I remove the rear plates where the dampener rubber is held. I placed 2 large 3" diameter washers on each side between the mount and the dampener and bolted the acces plate back on. Now the problem was moved to 65mph and was much less apparent.
Now comes the story. I looked up the mounts in my EPC (electronic parst catalog) and got the number 126 330 11 xx (don't remember the last two digets. I placed that numeber in my dial system (a larger version of the Worldpac Dial system that is fastlane) and the number converts to 126 330 13 xx. Strange, so I called my MB dealer and asked for two 126 330 13 xx and they don't have any. Real strange (this is the best moving 126 front end part). I ask if he has the 126 330 11 xx and he doesn't have them either. I ask him to look them up again and he also gets the 126 330 11 xx (but doesn't have them - I guess they just don't work on 126 cars any more). He orders me two of each number so we can compare. They are almost identical with only a two diget number stamped into the metal back plate as the only difference.
Next I compared them to the Febi/bilstein ones that I had in stock. The rubber was obviously less than half as stiff as told by my durometer reading thumbs. I used the 126 330 11 xx mounts in the car and absolutely fixed the problem.
We fix this notorious shake in BMWs all the time by using stiffer compounds in the longitudinal strut rubber. Some times its a cut down bushing from a larger car (E32 750 bushings cut to fit in E34 5 series). Some times we use urethane bushings made in the after market. I have been experimenting with the urethane bushings on the same position on 140 chassis that have so much problem. It absolutely fixes the problem. The bushing doesn't hold up though and we are redesigning one right now using two small wheel bearings instead in an aluminum housing. haven't tried it yet.
The point to all this is, when it comes to anything using rubber structually, BUY IT FROM MB. The fact that I picked out this vibration problem quickly was the only gratifying part of doing the job over for free.
One more interesting part. Since both numbers were currently available, I asked what the 13 xx was for. He couldn't tell me. I looked it up in the EPC that I have and it showed that the 13 xx number was used in almost all 126 bodies - not intended for the USA. I am a little confused why the aftermarket mounts are sold under the euro number rather than the US number. I can tell you that the US number is more costly. It seems to be the stiffer one also.
Bosch Master, ASE Master, L1
33 years MB technician