Mobil 1 7,500 mile oil and filters in all 3 DD's. I'm with Rick, no one has changed any oil or filters, engine or trans, for me for over 30 years and that includes the semi's that hold 8 gallons in the pan and 1 gallon in the filter. The Cat's got fresh oil every 10-12,000 miles.
About 10 years ago, I had over 300 gallons of drain oil and finally found a guy with a waste oil heater to take it...
Right now I have about 15 gallons I need to take to the recycle center.