Replaced plastic lines on 606, still sucking air!

[muleears]

I took the car in because it was nearly impossible to start when warm, most of the clear fuel lines had large bubbles in them.
So I spent almost $500 having my indy replace all the plastic fuel lines and O rings on my 98 W210. They also replaced the heat exchanger(?) and fittings.

Now, the next day, it is doing the same thing. Needless to say I'm not impressed with my indy's diagnostic ability, but what else could it be? He thinks it is leaking air farther back toward the tank. I wish I could post a pic but he has the car. I know the line from the filter to the banjo bolt on the back of the IP had air, come to think of it I think three had air. Once the car started it ran fine except for hesitation on hard acceleration. When shut off the fuel would drain out of the lines quickly. Once it started there was little noticeable air in the lines. Where do I go from here I haven't got any more Franklins to spare