slant 6 oil weight

Amen to the lighter oil in the 7.3L and 6.0L in winter!

Can't explain the 'don't use synthetic due to leaks' in this day and age. When Mobil 1 first came out in the 70's, only lighter weights were produced and older engines did have some leaks. But the newer variety of synthetic weights has fixed that; it is just 40+ years old old experience hanging on.

I run almost 100% synthetics in gas and racing engines but use dino oils in my 2 diesel trucks and just change it a lot. The protection that synthetics offer if something happens in the engine to drop pressure is very real. But it is not for everyone if you are on a budget (though the cost difference has gone down) or are working on the engine.