The first thing that I did on the day was to remove the “dry side” fuel hose that returns to the main fuel hose. I expected that there would be a bit of fuel to leak from the accumulator but was surprised that the hose was free flowing from the hose.
I have only had experience with the 6.9 that has a check on that line. It appears that the line on the 300E just Tees into the main fuel line. (Part no longer available)
There is signs of leaks from the banjo bolts so I attempted to tighten the 17mm fittings with a lot of pressure and it didnt seem to budge.
As I said before, I decided to button it back up and get the copper seals to replace and properly rebuild the system. Now however the car runs like new.

I am interested in the vacuum test.