w123 240D low speed steering wobble
 

My '81 240D has a noticeable front end wobble from the time you start moving until about 25 mph or so . After that it smooths out and is OK up to my normal maximum speed of 65 or so. It's very much like having a big bulge on a tire of the kind that forms when the tire is very worn, except for smoothing out at higher speeds. I just replaced the steering idler arm bushing which was loose. The tie rod and center link joints are all tight. The wheel bearings are plenty tight and well greased. My main suspect is a sticky caliper piston. The passenger side rotor drags pretty strongly against the brake pads when you have the wheel off and are turning it by hand (compared to the driver's side which turns freely). The only thing I've tried so far is to remove the pads from the passenger side and spray a bunch of brake part cleaner around the pistons. Obviously it wouldn't have penetrated very well and when I reassembled and test drove it, it was the same. Before I buy a couple calipers, can someone suggest another cause or confirm this as a likely one?