CM870 oil sample...

[Pete1990]

So i've been losing coolant.. My coolant lose is about 1 gallon every 25-35k Miles.. I change my oil at 15k... My recent oil sample came back with Higher numbers.... I had a shop pressure test my system we found the coolant filter was leaking. Replaced that then the system held Pressure just fine.. Where should i be looking next? This is getting old and i don't wanna keep spending money just to have a shop say sorry we don't know just run it....
This is on a 07 CM870 with welded EGR cooler and delete.. Miles on engine are almost 900k now.....