Todays diesel fuel has less sulphur. Sulphur added lubricity to the fuel systems and parts. I use opti- lube XPD additive to my fuel every fill up. My engine does not require DEF. It's an 06Duramax with 100K miles. The cost to replace the injectors on my engine is 3K. The additive, in my opinion holds that off a bit longer. A 60 dollar gallon lasts me a year. 3 oz per fill up.
Keep your fuel filter on a regular schedule. Diesel contains a bit of water. I purchase from stations that have a good turn over. Now the diesel is a renewable blend. i find my mileage has decreased since the switch over.
From the California resources board :R " Based on experience from other countries, equipment manufacturers and consumers have expressed concern regarding the lubricity of California diesel fuel as sulfur levels are further lowered. Unfortunately there is no currently accepted standard used for lubricity by the industry, therefore a lubricity standard has been included in the ARB’s proposal. "
So basically they don't know yet they say they included a standard. So what is the standard. :h