Hey yall, just recently changed my differential oil after I believe after 60K, because I believe the last time I did it I had around 260-270K miles. Now I have 315,000 miles on my 86 van 2wd. My mechanic put 80W90 oil in the differential and while I feel that the vehicle performs a tad bit better there is a slight humming noise that I have noticed. I took it back to my mechanic and he said it was a diff noise because its so old. He said probably all the debris/etc that came out of my oil change is the reason there is a slight noise now with new fresh oil. He was telling me that companies make a oil additive product which you can put in side diff to quiet it down, I believe it may thicken up the oil. Im really hesitant to additives etc, but I believe in this case it may be fine? With the mileage and everything into consideration, what do you guys think? Keep on driving it without adding the additive or what?