If I turn sharply especially to the right (it seems), the steering doesn't return to 'center'. I have steer it manually back to center. What would cause this?

Your car needs an alignment. The best place I found was my local Mercedes dealer- they were 20 dollars cheaper than anywhere else in town, did a good job, and hide a nice waiting room with free coffee.

Your front suspension is out of alignment, it usually doesn't change dramatically for no reason so first you have to figure out what happened. There is a very good possibility that your control arm bushings are worn out or some other component is damaged. Put the car up on jackstands and check it out thoroughly before making the appointment to get the alignment done. If you have recently replaced some front end components then that is almost definitely the reason for what is going on.

Have you messed with the steering box?

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83 300SD Dark Silver Dark brown inside

If you adjust the steering box to much it will not return to the center.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

I just replaced the struts, strut mounts, and the center link. Maybe that's the problem. Seems like it was this way before, though....but I can't remember.

It would help if you listed what kind of car you have. As W123 dont have struts.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

You need to adjust the struts, they're probably not equal to the previous measurements. The struts and mounts are responsible for caster primarily, as well as a bit of camber and toe, according to some of the old threads here.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

1995 e300d w124.