Does this engine have a coolant filter??? Mine does but I know that at some point Cummins did away with this.
I bought my coach in 2008 with no maintenance records, it was a repo, but from the condition of the rig it appeared like it was well taken care of.
I checked the coolant with test strips and changed the coolant filter every ~2 years. But I lost confidence in my ability to read the strips, actually got a quote from the local Cummins shop to do a flush and change but the manager recommended I get the the coolant tested, this was in 2015. My guess was that the coolant was original so it was ~14 years old. But the coolant analysis came back great, as if it was new.
So for that coolant to show that condition there must be something seriously wrong. I guess you could take a chance on it and spend to get some sort of good warranty but there is a risk. Either way the engine needs to have a good flush and new coolant added.
I late 2015 (yes, right after I got a good coolant analysis report back) road debris took out my radiator. Got a new radiator installed and Cummins used the ES Compleat blue coolant. Manager recommended this and said this would last the life of the rig. https://www.cumminsfiltration.com/eme/hybrid