I had the same issue with my 129. I thought trunk too. But then I jacked it up and pulled the cover off the pumps/filter/accumulator and sure enough, one of the fuel filter connectors had a very minor leak. Tightened it up and all was fine.

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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