Haven't really done anything to my '99 E300 with 200K on it in awhile other than regular maintenance like oil changes, as it hasn't really called for anything.

Noticed my delivery valves are leaking at the top and are wet. The brown lines from the fuel filter are wet and the shut off valve is wet, and it leaks from the back of the pump onto the ground and leaves diesel.

Surprisingly haven't noticed a decrease in fuel economy or any hard starts.

What should I replace while I'm in there besides what I've stated? Also, what leaks from the back of the IP on this motor? The IP is wet with oil as well in the back. What is that just blow-by from the nearby EGR? My car doens't use oil in 5000 mile oil changes.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

The rack return drain hose is between the block and IP on the inner side. It joins up with the injector return lines at the secondary filter purge vent to go back to the tank return line.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The lift pump on the side of the IP has a gasket which if failed, results in engine oil leakage. Mine is leaking from that point right now, haven't had a chance to replace it yet.

The "brown" lines are supposed to be clear. Brown = really old. I'd replace them all at this point. There are six in total. The shut off valve has an o-ring that needs replacing. Fryerpower.com has a complete set of o-rings in Viton, which if you're replacing everything anyways, is a solid choice. I just installed their o-ring kit on my 606 a few weeks back and cured all my leaks in one fell swoop.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

That'd be cool to replace those old lines, but can't find a part number for them or find them on one of the mercedes dealer wholesale parts sites. What's the advantage to viton rings vs MB?

That'd explain why my IP is leaking oil from the back.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

There is a wiki paper on replacing the delivery valve seals in a 1997 606 engine. It might be helpful to you.

PeachPartsWiki: Replacing the Delivery Valve Seals

The replacement plastic fuel lines can be found here:
1998 Mercedes-Benz E300 Turbodiesel Sedan - Fuel System - Page 1

The MB o-rings are made of nitrile (buna) rubber. Viton is generally considered as superior to buna, and has a reputation for lasting longer. There's certainly nothing wrong with the MB-spec stuff, but the Viton o-rings are a popular enthusiast upgrade.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!