I changed the oil. The Chilton manual says to remove the oil filter FIRST before draining the sump, so the oil from the filter can drain into the sump.
The o-rings at the bottom of the pipe that go from the cap down through the filter were worn, and I wanted to replace them. The local NAPA didn't have anything that would fit.
They are said to be 6mm IDx 2mm thickness. I was able to find them on fleabay, and will have some on hand to change them out next oil change.
I used Rotella T6 5w-40. It meets the CJ4 standard, which is supposed to be backward compatible with the old CD spec that the Chilton manual calls for.
Edited to add: this oil meets the newish Ford spec WSS-M2C171-F1, which not all the CK4 oils meet. That means it's more likely to have adequate phosphorus to protect our cams.