An update to this...I bought the part from the dealer and replaced it. Very easy repair. There was initially some vibration and noise at idle after the repair, but substantially less than before the part broke. Since I made the repair the noise and vibration at idle have been getting worse again, and now they are as bad as they were right before the spring broke. Any ideas what could be causing this? Could the shock be failing? Any ways to test the shock?

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2006 E320CDI- current dd
1999 E300TD - retired
Wilmington, NC USA