I have a 1983 300D with 68k miles on it that has had a clunk ever since I got it. I have replaced every single wear item in the front end. Upper control arms (ball joints and bushings). Lower control arm bushings. Tie rods, drag link, steering shock. Shocks. Idler arm bushing. Lower ball joints. Brake support mounts and bushings. All of this work got rid of most of the clunk, but if I move the wheel quickly right or left I still have a clunk.
BTW, my steering box mounts were a little loose (started turning at 40 lb-ft). I tightened them up to 60 lb-ft (upper limit of spec per CD). Are W123's prone to cracking where the box mounts like some older cars?