I checked and most if not all underhood fuel lines are 5/16 and are attached with the original fuel injection type clamps.

The fuel filter may be from 2014, but I think I have only put 8,000 miles on the car since. I can't remember whether I replaced the o-rings or not, but I'm guessing I did because I'm usually pretty good about replacing any seals I come across when servicing other parts -- yesterday I found a metric o-ring assortment in one of my boxes of Mercedes parts from my last move that would have been packed up shortly after replacing the fuel filter.

The first order of business will be to find some metric line to buy to replace all the new 5/16 line. I thought that the stock line was 7.5mm though?

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.