My # 5 injector (I think it's #5 - closest to the firewall) had diesel leaking around it, but I couldn't see from where. I replaced the return line, which was brittle and cracking, but the leak persisted, enough to affect my fuel mileage. Then I noticed that there is a short piece of hose with a plug in it on the other side of the injector. I had snipped off a piece of the return line for #5 injector and had a small piece left. Replaced it and no more leak.

Some of you guys probably know this, but I wanted to pass it along - when replacing your return lines, don't forget the the #5 plugged line!

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer