I always use 15/40 for diesels,
zinc additive.
On the first cruise, which I ever took the car on, this happened;
to the rear main.
Fortunately I was easy on the car, and nothing else was wrong. We did a lot of checking to see where things went wrong, and also did a lot of preventitive work.
Engine builder stood behind his product, but I still had to re and re it. I'm glad 2010 is over LOL