I had a similar problem on the rear of a non-MB, including the lateral wobble at low speed, that took me quite a while to diagnose. I too went through the exercise of balancing and re-balancing the wheels at different shops, verifying that the unloaded outside diameters had no lumps, and so on. It turned out to be a broken belt in the tire (I was eventually told), visible only as a small, shallow crease in the sidewall. You'd think a tire shop would pick this up first time, but they didn't. Two new tires solved my problem. Like the CLK, this car has stagger, and in this case I didn't have enough front clearance to swap the tires front to rear. Have a close look at both sidewalls. If it's feasible on the CLK, you could also try swapping the tires front to rear to see if the problem changes axle.