Used oil analysis would give some better information. I looked up Delo to see if they made an 0w-40 as Walmart is not stocking any more and parts stores want way too much. Can get 5w-40 Synthetic which may work as well. I don't know the price yet but will check it out.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles