Does Blackstone do TBN and TAN, and maybe charge extra for it? In our extrusion presses, we had anywhere between 2000 and 3500 gallons of hydraulic fluid (depending on the size of the press), and we took monthly samples (with TAN twice a year). For viscosity, zinc (anti-wear), and other beneficial elements, we could throw in additives. We had kidney loop filtration systems running 24/7 to keep solids out. Unless a water/oil heat exchanger in our cooling systems ruptured we didn't have too many issues with H2O contamination. We even had a centrifuge to separate water from the oil.
But, if the Total Acid Number got too high, (you can't filter acid out of the oil) we had to change the oil - very expensive. It's not a good day when you see a couple 10 wheeler tankers pull up behind your press!
IDK if TAN will apply for our trucks since we change the oil fairly often but, just a thought...