Most if not all system uses the secondary fuel filter and the lift pump with WVO or diesel. They are singleton in the car. You have 1 feed line and 1 return line so you only need 2 x 3-way valves. One at the feed and one at the return line. WVO and diesel will mix during switching, within IP at least even if you add separate electric lift pump. There is no way you can prevent it.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.