A quart of Marvel Mystery Oil added to the fuel tank

Danger Will Robinson! Marvel is like atf with valve grind compound added for abrasive cleaning. It will accelerate the wear of your injectors not make them last longer. No offense Diesel4u, just saying so you can check it out and decide if you want to stay with that program.
Metro, whatever you use, put it in every tank. Your injectors can't remember that you put lube in the fuel two tanksfulls ago unless you just added a little to top it off and there was some mixed in.
I trust Marvel Mystery Oil ,its been around for a long long time,and I doubt they would reccomend using it in diesel fuel if it had any potential for harming the engine or injectors,especially in big rigs,if it did any harm they would have been sued out of bussiness a long time ago--they tout it as a substitute for the sulpher taken out of todays diesel fuel right on the can.........dont know where you heard it has valve grinding compound in it either,though it does have similarities to ATF,its a lubricant as well as a solvent,with a film strength higher than many thick motor oils...
My truck has only had a few quarts of it added over the past 10 years,as I do not drive it much on the street,it would take me a long time to wear out any injectors at that rate using it...I have added a quart of Marvel Mystery Oil to the crankcase oil in many of my vehicles over the past 35 years and never had any problems resulting from its use,I liked to change the oil when I bought a new to me vehicle and add the Marvel to it,run it 500 miles or so,and change it again...