It could be a leaky seal at the electrical connector, or could use a fluid change. I have a simliar issue with mine, it comes and goes. I think dealers will steer you away from changing fluid, they dont want you coming back and saying its worse than it was before..... See if you can find an independent mechanic that will change it for you. Make sure they use MB Fluid ONLY!!!

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Dennis
2006 E320 CDI Black/Black Leather. Nav, HTD Seats HK stereo 32000 miles.
2000 VW Passat 1.8t 300,000 miles as of Dec 09, 2009 original owner
1997 E300d Silver 300,000 miles As of Jan 05, 2010
3rd owner SOLD