The key to longer oil life comes down to how well you condition your oil, which means keep it clean and keep it cool. By the time I had spent two years maintaining heavy equipment in the middle of the Sahara (Libya), I was used to changing fluids often as we struggled to keep oil temperatures under 240-250F on our oil exploration machines. Shortly after that I had the opportunity to work with a former NASA engineer while we were developing more advanced hydraulic systems and his experience taught me that lesson about how it's not how much oil you have, but how well you condition it. He was a walking knowledge bank when it came to hydraulic system design and we went on to implement lessons he learned from the Apollo program to our machines working in very hot climates. He often commented how they were pushed to very efficient designs due to space constraints and payload. Rather than increase the fluid volume, we focused on better cooling and filtration and used just enough fluid to keep all components satisfied, kind of like the radiator is both the cooler and reservoir and we used a small tank for a fill point (like a radiator uses a smaller overflow tank). Our maintenance budget and fluid changes dropped a bunch. I used this approach on a previous truck I had and rather than upping the trans volume with a big oil pan, I focused on cooling and increased the cooler to the largest one I could possibly put in front of the truck. Before the cooler my trans ran right around 210-220F when hot, but after the cooler upgrade it was never over 180F, even when towing. The same can be applied to engine oil cooling. I sold the truck with 260,000 miles on it and it was still the original transmission and engine, and both were working very well. Better filtration keeps the fluid clean, and avoiding high temperatures prevents the breakdown of the additives. Beyond that, the other factors working against fluids are water (can lead to acid formation), and shear breakdown from high forces. There's such as thing as overcooling too, just need to make sure the fluids stay warm during cold weather.