2002 E430, 37K miles. Noticeable decrease in fuel economy since January but no driveability issues or CE light. Presented to dealer 2 months ago but "no faults found" Occasional stumbling now noted, particularly during shifting, in past 3 weeks; return to dealer again finds no faults.

Now, with vehicle literally just out of factory warranty, engine oil analysis reveals excessive fuel in oil, with less than 3K miles on oil since last oil change. Dealer doesn't want to cover issue, saying vehicle is no longer warranted.

Recommendations? Complain to MB-USA? Escalate to a zone rep?

Any idea as to problem - leaking fuel injector? Both cats have been renewed, under warranty, due to internal rattling.