Try Euro Motorcars in Bethesda. I have heard good things about them. Or, if you don't mind a drive, try McGeorge Mercedes in Richmond, VA, about 1 hour south. McGeorge just did a 4-wheel alignment on my S420 ($125 US) and they did a great job. I wouldn't hesitate to go back.

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles