I know we are talking different models here, but I replaced a leaky fule line on my W124 a few months ago.

My only real preparation was to depressurize the system...translation: open the gas cap and let the "woosh" occur.

I also clamped down the hose leading from the tank with a pair of vice grips to be sure. I only lost a few ounces of fuel during the installation.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car