Snoboy,
I send the tractor and truck oil off to Blackstone. The JD oil has only gone a couple times. The truck I send if I let the oil go longer than I have in the past. The last oil change on the truck was well around or under the milage I changed last time so I did not send out to be tested. I have run the oil to about 8,000 miles I think and Blackstone said to go to 10,000 and see what happens.
I don't want to go that high but at least I know it possible on the oil. I am using Shell 5w40 in the truck and the last oil change the tractor got the same oil.
I will send the tractor oil to be sampled again.
Later,
Dan