Here are the part numbers for all the fuel lines. They have an oring on each end that dries out and fails. On occassion, the lines themselves get brittle and crack. The lines are clear when new and are yellow or brown when old.
http://detali.ru/cat/oem_mb2.asp?TP=1&F=210020&M=606%2E912&GA=722%2E438722%2E600&GM=717%2E446&CT=M&cat=19T&SID=07&SGR=120&SGN=04
To remove, push the white horseshoe clips tightly closed (e.g.: make a ringer) to release the clips holding the fuel line to each fitting. Takes a pretty firm tug to get them off. Once off, install new o-rings or new lines (new lines are$50-$60 for the set and come wiht orings installed).
Shut off valve is held in place by two torx cap bolts and has 1 o-ring seal between it and the IP.
Delivery valves have an o-ring and a crush washer. Requires a special MB splined socket to remove. Ask for MORE HELP if you plan to tackle this job; while not difficult, it is a bit techinal and there are some major cautions to be gone over first.