With leaks around the delivery valves, I am installing the viton O rings (from Jim at fryerpower.com) on them and replacing all of the O rings at the same time. To echo others, thanks Jim for your packaging of them well identified on a piece of paper, instead of just placed in a baggy and we are on our own to figure it out!

Mercedes Benz designed the fuel return lines with the fabric wrapping so that when the line eventually cracks from age and heat, it will merely leak instead of breaking open with fuel spurting all over, and maybe leaving you out of fuel somewhere. The viton return lines do not have that wrapping, so when they eventually crack, fuel will spurt out.

It is not a problem to check those return lines weekly on the 601, 602, 603, and older diesels, but the 606 has a cover over the valve cover which blocks quick access to the return lines. So my only warning of a leak from a crack will be after the fact.

Any other 606 people have thoughts/concerns about this?