Jaymus,
I'm totally sure this was RTS 5w-40, the newer CJ4/SM one, I still have the bottle.
The only thing that I can think of: when I filled the oil filter up with oil before installing it, I filled it with Castrol Syntec 5w-20, left over from my girlfriend's Honda.
It would have been about an eighth of a quart of Syntec 5w-20.
Would an eighth of a quart of 5w20 change the Ca, Zn and P that much?