Engine Oil Discussion

I'll add my personal experience.

Worn out engines benefit even more from synthetic oils. They're usually worn from neglect and owners being cheap. They tend to continue wearing rapidly because nothing is where it should be. Pressure is low, clearances are huge, volume of flow is down, and finishes are often sub optimal and higher friction. Getting a better, slicker barrier in place helps limp along before it finally gives up. Typically they'll soak up more contaminants too due to better additives than the cheap junk on clearance at the local discount hardware store.

If you want an excuse to rebuilt it, run some cheap *** farm fleet bulk oil, or better yet some recycled junk that's cheaper than canola oil, and then act surprised when you're picking up bits off the side of the road.

I've put synthetics in everything that are past broken in and have never found the old wives tales of leaks or burning to be true. If anything, synthetics have helped pull sludge and junk from inside everything from my tractors to lawnmowers and even high mile beater motors. This makes them far less gross to deal with when it comes time for an overhaul too.
Every leak I've experienced has been due to cheap gaskets, parts prepped with a hammer and chisel, or so worn by horribly hard seals that nothing would stay behind the rubber. Early synthetics did have more issues, but technology has marched on and and in over 20 years of using it, I've yet to have it be the cause of a single issue I've ever run into. If anything it has saved me plenty of motors and turbos that suffered momentary oil starvation, because when I did try to cheap out when I was super broke those same momentary losses of pressure killed engines and turbos so quickly it was a joke.

Everything I've run conventional oil in looks the same inside: like trash. Dark, grimey, and as if was filled with bearing grease then cooked over an open flame. If conventional oil fixes mystery leak, it's because it's plugging shitty assembly practices. There's a reason Bubbas motor always looks like it was recovered from an oil slick "but doesn't drop a drop!"

Synthetics can also golonger between changes, making cheaper oils a false economic saving. Unless the stuff pours out as fast as you're pouring it in, synthetics will likely be break even at worst.

It's true that some people simply don't have the option to run what's optimal, but to suggest against the best potential solution based on old wives tales is a joke.

Also, anyone claiming it doesn't matter if oil unlocks more HP misses the entire point. Any power consumed by the oil is the result of heat and friction, which we can also consider wear. Most people won't get this though.

Hopefully OP gets many more miles from his Slant. He'd get the most though from a decent synthetic that's slightly heavier than the original spec (to help with worn clearances, assuming idle pressure is suboptimal).