Liner O-ring failure

[Truckdriven]

I have a 2017 CM2350 720k mi. that I just purchased and within 2 mo. started losing lots of coolant, turned out to be a failed O-ring on #2 cylinder liner on the exhaust side, Even though all the internals showed very little wear I am doing a full overhaul with all the extra steps this forum teaches. What keeps rolling through my mind is why did the o-ring fail? The abuse history shows the highest coolant temp was 230 for less than 2 minutes so doesn't seem that caused it. If I go all out on a rebuild how can I prevent an early failure putting me back in the same position? It does appear like it had waterless coolant at some point before I had it as the inside of the block looks rusted but is actually a brown film with the texture of dry grease that can be wiped off. Also I had a transmission heat exchanger fail mixing lots of gear oil in the cooling system and I've seen engine oil and coolant mix deteriorate rubber hoses, seals etc but didn't know if gear oil does the same? Also the o-ring looks like it was falling apart long before the trans cooler failure. I will attach pics