Steering "darty" PLEASE HELP!

[cscmc1]

This is driving me nuts now... my W124 300D is darty as can be at highway speeds. It's scary to drive over 50mph! I have replaced sway bar bushings, rear subframe bushings, and drag links. Shocks and struts are relatively new. I need to get an alignment next, but eyeballing the front tires, the only this I notice is that camber is probably zero (or even slightly positive). Another thing I have noticed is that the steering will NOT center itself after a turn, which I am sure contributes to constant input being needed on the highway. I can't feel any slop in the front tires when the front is jacked up, and backing off the load adjustment in the steering box doesn't seem to help much; I thought maybe someone had over-adjusted it in the past.

Any ideas? I am going nuts here! I'd just spring for an alignment, but I want to make sure I have changed all the suspension items I can before I shell out the bucks for the alignment. FWIW, I bought this car in April and the steeirng wheel was off-center from the time I bought it. Botched alignment last time 'round?

Thanks all!