James, a reputable MB Service Department should do whatever it takes to diagnose what is causing the pulling problem with your 300D, especially since they have aligned it twice in 6 months. I would call the Service Manager, explain the pulling problem in detail, and request that they diagnose the root cause of the problem. Typically any good alignment shop will thoroughly inspect all suspension components before doing an alignment to ensure that they are not wasting their time and your money.

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Fred Hoelzle