Stop changing your oil!

A friend of mine has a 76 Toyota Chinook, 20R. He hasn't changed the oil EVER on it, and it still seems to run strong. We drove it to Fort McMurray AB, from Vancouver Island, and all the way back, as well as plenty of other trips, and have used it as a daily driver. Oil is blacker than black inside, but the thing just keeps on going. Probably has 250,000 miles on it. And who knows the previous owners history.