Amsoil full synthetic and their high-end filters in everything for almost 20 years here - I change the oil once a year whether it needs it or not...
When I switched the Mustang at around 140k miles I dumped their cleaner in the crankcase with the old oil and a new Wix filter, ran it per instructions, that new filter weighed two or three times what it did full of clean oil, and the old oil was pitch black. Right away it smoothed out a bit and ran a little cooler.
Up until about 2017 I was putting 12 to 15,000 mi a year on it driving it like I stole it, when I changed the oil each year it barely looked used.
When I switched the Mustang at around 140k miles I dumped their cleaner in the crankcase with the old oil and a new Wix filter, ran it per instructions, that new filter weighed two or three times what it did full of clean oil, and the old oil was pitch black. Right away it smoothed out a bit and ran a little cooler.
Up until about 2017 I was putting 12 to 15,000 mi a year on it driving it like I stole it, when I changed the oil each year it barely looked used.