Great site here, been spending lots of time reading other people's tech troubleshooting and detailing tips.
My family has an 87 300E, with just a touch past 170k miles on it. About a year ago, I began noticing that the steering wasn't quite as solid as it used to be - the car would feel like it was wiggling a little bit at highway speeds (~60-75 mph). Last thanksgiving, on a trip to the bay area, i noticed that there was a correlation between how far the accelerator was depressed and where the steering wheel centered; at speed (~70 mph, ~3000 rpm), depressing the accelerator recentered the steering wheel about an inch to the right of where it should be, letting up on the gas moved it back to left. This was fairly consistent, i did it a few times before deciding i had tested it out enough.
Soon thereafter I stopped driving the car on a regular basis; my father took the car into the dealer, but they couldn't find anything wrong with the steering. A couple of days ago I had the chance to try the car out again, and while the steering no longer moves around with the position of the gas pedal, the car still feels wiggly. I had the opportunity to more or less floor the gas while merging into 50 mph traffic, and it felt like the car was swaying left and right as i passed through ~4-5000 rpm before settling down to a normal cruising speed.