Diagnosing front-end wobble on '89 300SEL

[Brett24]

I'm having a spot of trouble diagnosing the cause of a front-end wobble on my '89 300 SEL.

It started as a mild wobble, but has progressed (over about 3-5 thousand miles) to the point where the car is essentially undriveable. The wobble hits around 50-55 MPH, then doesn't go away again until I slow down to about 30-35 MPH. As I live in a rural area, and exit my driveway onto a highway, I need highway speeds every time I leave the house.

So far I've replaced wheel bearings, tie rods, and (very worn) guide rod bushings. I have six mounted tires for that car, so I've tried all combinations of tires on the front. Nothing, so far, has seemed to help. (Taking it to a front-end shop is very much an admission of defeat for me, so I'm not ready to do that yet.)

The boots on lower control arm ball joints are in bad shape and the ball joints are visible and rusty. But doing a test I found (while searching the archives) that checks for ball joint play, the ball joints appeared to be without play/slop.

Any thoughts, pointers, ideas?

Also, I have a 12-ton shop press, and spring compressors. Is there anything else I would need to be able to replace the ball joints? (I've never done that job before.)

Thanks.
Brett