15w-40 VS 10w-30

Your may want to try what I did. Both my sons and my wifes vehicles had main seal leaks. Just regular gas vehicles. I found at Canadian tire in liter bottles, a rear main seal repair additive. There were two types, one worked a bit, but the other worked great. I will have to look up which for you. Anyway, on my last rig it started leaking pretty hard from the main seals. Both! I tossed 6 bottles of that stuff in there. After about 100miles, it never leaked again. All 3 vehicles were fixed. On research, the theory is the seals get hard and brittle from petroleum products. THis stuff is like armour all , it replenishes the rubbers and makes them soft again, and they claim they regain there shape or swell if you will. What ever it does it worked great and is still working. THe rig is sold, but I put a lot of miles on it with no leaking, and was not leaking when I sold it.

 

I used Lucas rear main seal a few yrs back, it worked for a few months.Soon to be replaced, the front seal, seeps, no drips. I changed o rings on oil cooler 5 yrs ago. They crumbled, into pieces. Post the product if you remember, I recall people using brake fluid, along with a little sawdust for rod knock. Lol