Note I don't know if the below is the correct size info. Perhaps you could pull of one delivery valve holder and measure the O-ring and get some approximation of the size.
If you look up the Mercedes Part number for yours and the Mercedes Part mumber for the 606 that would narrow down the answer.
I've had no luck with Jim. He had a fire I saw in another thread and wasn't gonna be able to send any out. so I just got a bunch from mcmastercarr. I ordered extra to have in shop. I gotta check out how much they were but can mail you a set. I also got Viton fuel return lines. I could send you what you need.
This is what ya need more or less. You also need the copper washers for delivery valves if you do those. Not a bad idea while you have the intake off. I think I have 6 of those too.
*O-ring sizes for 606 *Diesel*
1 shutoff valve 2.5mm x 12mm ID
9 fuel line 2.5mm x 8mm ID (1 located at fuel filter housing)
3 fuel filter housing 2.5mm x 10mm ID
1 pre-filter 3mm x 18mm ID
6 delivery valves 2mm x 15mm ID (60x delivery valve )
4-5 feet Fuel return lines 1/8 ID 1/4 OD 1/16 wall
99 e300 diesel fuel line o-rings
http://www.peachparts.com/shopforum/diesel-discussion/362724-99-e300-diesel-fuel-line-o-rings.html
This has a list of threads that have information but for sure some of it is out of date.
“Viton hose and O-ring kit sources”
http://www.peachparts.com/shopforum/alternative-fuels/300684-viton-hose-o-ring-kit-sources.html#post2738467