This is what I would check. Use a meter to ohm out every glow plug at the GP relay. GP light on doesn't mean all 6 are working. It could be 5 or 4. If all 6 are checked out then crack open the injector nut one at a time ( 14mm spanner ) and crank the engine. If fuel spills out then the fuel system is fine on that line. Retighren the line and check next one. There is not much to no start if the car had been working fine previously.

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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.