Where should I start to look for the cause of my right mirror to stop dipping when in reverse? Looks like fuse 4 under the rear seat controls it, but everything else on that fuse still works.

2001 E430.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport