The oil I use I became a
The oil I use I became a dealer for to both reduce my cost and allow me to provide it to others at cost, so I have no doubt my comments will be viewed as skewed, but in the 80's I was a mechanic at a Corvette specialty shop (and high performance boats) while in high school and the owner was an Amsoil dealer. It was the very first API certified synthetic oil, but I didn't know anything about the brand (had never heard of it or synthetics before despite doing oil changes since age 8 in my grandfathers Mobil gas station and fixing cars practically all of my life). All I knew about it from that time was that it was "synthetic". We actually never referred to the brand internally or with customers, just that it was synthetic and much better than regular oil. Of all the things I did in that shop, oil changes were very few and far between. We did all sorts of repair and restoration work and built many ridiculously high performance engines (for the time) from the ground up (that scared the crap out of the owners after picking up their newly repaired car), they all got synthetic oil once a year, and we never had any cars return for lubrication-related issues (which many times can mascarade as cooling system issues).
I forgot all about the Amsoil brand and used many others over the years, but found a "data point" in the oil life monitor of a '91 Corvette I had when I lived in Germany for a few years (many hard Autobahn miles and it rarely saw time below 100mph). I tried the different synthetics I had access to and Castrol Syntech was the oil that would last the longest, but I found out many years later that Syntec started with a synthetic base then switched to a dino-oil base to reduce cost, so I don't know which version I was using, but it worked well.
I have many anecdotal stories personally from 15 years in military aviation (using lowest-bidder synthetics in helicopter gear boxes and turbine engines with rigorous oil sampling), and from many years of connecting with others about their vehicle maintenance, but going back to the beginning of what really sold me on synthetics was an incident that happened to the owner of the Corvette shop (Bill if you're reading this, yes it's me). While coming back from the lake towing his flat-bottom circle-track racing boat (heavier than you would think) with a 454 that could turn over 9,000 RPM, his lifted 1st generation Jeep Cherokee with a stock AMC 6.6L V8 lurched and the engine started "missing" on one cylinder. He looked back and saw oil all over the nose of the boat and figured he would be stuck if he stopped so the further he got before the engine seized, the less the tow back home would cost. It was about 15-20 miles home from that point at highway speeds and he made it all the way with no oil pressure. I saw the Jeep and boat outside the next day (the boat was almost never left outside) and asked what the deal was. He told me the story then said, "Go check out the oil pan and see if it starts, and if it does then pull the boat in." The oil pan had a huge "smiley face" ripped through it (threw a rod but the piston and rod pieces stayed logged up out of the way of the crankshaft), and when I got in it started up with no hesitation at all. I drove it around, backed the boat into its parking spot and pulled the Jeep back where it normally goes. Other than the oil light and the sound of the engine missing on one cylinder, there was no indication of anything wrong. We built a very nice Chevy engine for the Jeep, and when we disassembled the AMC engine there was absolutely no indication of excessive wear on bearings, cam lobes, lifters, or anything else -- that was what sold me on synthetics.
It was ironic that after I used Castrol Syntec for so many years, it wasn't until they started running the ads where they drained the oil out of running engines and showed them seizing using other oils that I recalled the incident with the Jeep and switched to using Amsoil myself.