[Bangaway]

The line coming off the prefilter (606 motor) leads to this black plastic thing--line 70/4 on page two-- http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/Maintenance/94_95/0781.pdf

What is this plastic thing that this fuel line goes to?

 

[sbaert]

That line goes to the fuel heater/thermostat located inside the coolant passage of the cylinder head.

 

[Bangaway]

I noticed a little seepage here. Is this a known leak area? What should I replace to fix?

I think this is it. http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/Engine/605_606/07.1-5620.pdf

Where would this thing leak?

 

[sbaert]

Could be a leaking fuel heater or associated gasket.

Also keep in mind that all of the fuel lines are prone to leaking on this particular model.

If your lines look brown or black, replace them all especially if you still have the old style with metal clips. Get the updated lines, especially the one that goes on the back of the injection pump that replace the clip style with the reliable old style banjo fitting and associated bolt.