you cannot buy the O rings for the plastic tubes from mercedes. You can buy them from an industrial O ring supply place though. But that only works if the lines are still serviceable, if they are cooked a dark brown color - replace them.

to remove them - press the horseshoe inwards to unlock the line. Do this on a hot engine and replace 1 line at time and fire the engine after every line. this will prevent air locks in the system.

Get a can of lubro moly purge and clean out the fuel system, you will need to disconnect the feed line which is buried under the intake manifold (its tightened to the fuel heater in the head)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)