Coolant in fuel water separator

[tree98]

It's most likely to be a bad injector cup. Cummins has a repair for this but it's not a guarantee, they are rings that get pressed down into the cup with a special tool. You do all 6 injector cups even though it's probably only 1 that's leaking. If that doesn’t fix it you'll have to replace the head.

https://youtu.be/pVC2OF83r-k?si=Gd0X42_1vDU04X-Y