My 190D is leaking fuel out of the top of just one of the injectors..
Its not the braided return lines... did them already!
Being a Diesel moron, I thought I better get proper advice before I mess anything up...
Crappy pic...

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2009 Mercedes ML320 Bluetec

If it's leaking from the injector halves, there is corrosion which can be cleaned - http://www.peachparts.com/shopforum/showthread.php?t=299321

If it's leaking from the injector line fitting, you probably overtightened the line and deformed the ball-and-cup seal. Further tightening might do it but start looking for a replacement line.

Sixto
87 300D

Not touched it aside from replacing the overflow lines, which are just a push fit.
I noticed a stain on the street where its parked, and on inspection spotted the leak.

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2009 Mercedes ML320 Bluetec

Is it one injector or all? Maybe you nudged the return line nipples and now they aren't on properly.

Sixto
87 300D

Just one leaking.
Now I see the way it all goes together, I will look at the return lines again... it looks too high up to be from the joint of the two main pieces of the injector.

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2009 Mercedes ML320 Bluetec

Some people us a Knife or other metal object to remove the Injector Fuel Return Hoses. This sometimes results in the Nipples being scratched or dented enough so that the leak.

Use of a Socket to remove and install the Injectors that is not deep enough also can tweak the Nipples.

The little nipples are swedged/crimped into the upper body and once in a while they become loose in the upper body and leak.
The fix for that is to replace the upper Body (that changes the opening/pop pressure) or as one Member did cut the Nipple off and weld over the hole and move the Injector to the End Cylinder.

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84 300D, 82 Volvo 244Gl Diesel

I had replaced the return lines about a year ago..
A closer inspection showed that the fabric cover was soaked with fuel.
I pulled off them both and sure enough the rearward one was broken... the rubber center was broken about 1/2" up.

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2009 Mercedes ML320 Bluetec