Yes, make sure you are suspending the car on the jack properly if you want to get an accurate assessment of ball joint wear.

I expect your problem to be a combination of poor wheel balance and loose steering linkage. Make sure you check the idler arm bushings while checking all the steering linkage. Additionally, ensure that there is no slack in the steering box, if so it can possibly be adjusted out.

Typically loose steering linkage will not CAUSE a vibration, but will amplify any vibration that is present. For this reason, you need to first ensure that your wheels have a good DYNAMIC balance. This means balance weights on two planes. It is all too common for MB wheels to get a static balance with weights only on the inboard lip. This is because the kids in the tire stores have been yelled at for scratching the outside of the alloy wheels. If you are sensitive about scratching the wheels, you should try to find someone who will use tape weights just behind the spoke area of the wheels. By putting weights there AND the inboard lip, you can get a good two plane, dynamic balance and vibration will be nil. Inboard weighted static balance prevents the wheel from hopping up and down, but without proper dynamic (two plane) balance the wheel will wobble. On the nimble suspended MB's this wobble will transfer a tremendous amount of vibration through the suspension. If the steering linkage is loose, the vibration will be a shimmy, shaking the steering wheel like crazy.

Good luck,