I have an oil leak that has just popped up on my truck. It is on the left side of the engine, but I can't really find where it's coming from. There is a metal line that goes into the valve cover that looks like it might be leaking, as there is some residue on the cover around and leading away from it, but I was thinking that line was fuel? Could that be the source of my leak, or should I look for something else?
It seems to only leak when the engine is running, but even with it running I can't find anything leaking enough to be losing the amount of oil that seems to be leaking out. It does not smoke at all, so it isn't burning oil.....
I read one post of a similar problem suggesting maybe the tappet cover, but I don't really know enough about diesels, and I can't find much in the way of description or help on that....
Also, I had the injectors replaced about 10k miles ago. Could this be something that wasn't tightened securely, and vibrated loose? I'm really trying to find out where to look...
Any suggestions would help greatly!

i think you're right...return lines probably leaking.

i think you're right...return lines probably leaking.

Would that be the metal line coming out of the cover toward the front? I will check it tomorrow and see if I can tighten it up a little, if that is the case.
Thanks for the response! I love this truck, but learning all about it is killing me......never had a diesel before, so thanks for everyone's patience with the newb questions...

Maybe try to get a picture? I believe it is a common problem so i think you were on the right track. Id check to see if fuel is mixing with the oil too, to be safe

Here is where it seems to be coming from. Is this an oil line?
It is on the front left of the engine, just in front of where the upper radiator hose runs, and just behind the left side alternator (my truck has 2 alternators).
Now I just have to figure out what to do to try and tighten it a little

I got started on this earlier, then decided just to leave it for tomorrow. Is there a seal or gasket I should replace on this line? I'm thinking there would at least be an oring, but I can't seem to find any kind of info on it.....