Shepard Machine was our Cat dealer. They offered a service to test oils for metal, carbon, sulpher, brass, etc. We pulled samples from eng, trans, hyd, dif, and final drives, labeled them and sent them in. Took 7 to 10 days to receive the result, which was put into the file.
Same service from pennzoil.
Some times we ran oil in the loco's over a year. If no dilution, or contamination why change?
Bruce
Works good
Lasts long time