As the title suggests, there is air in the fuel lines of my om606-equipped w124 (E300 Diesel T-Model, 124.191). I have researched this as much as I can and just need a few pointers. I can see bubbles in all of the clear plastic tubes, including the tube that leads from the fuel heat exchanger to the fuel pre-filter. Am I right in concluding that the air leak must be upstream of the fuel pre-filter? If so, am I right in concluding that the air leak must be either at the fuel heat exchanger or at the tank strainer or at some pipe join in between? There is no diesel on my driveway. Surely if the leak anywhere else, I would not be seeing air bubbles in the clear pipe which goes from the fuel heat exchanger to the fuel pre-filter? The bubbles appear to be travelling with the fuel (obviously, I suppose). Thanks for your help.