I am no expert... However, I often had lunch with one, when I was working in the Research Company of an oil major. The following shared wisdom is from the 90s, so take it for what it is worth...
- Use synthetic oils, they have better and more robust/durable characteristics.
- Oil degrades because of short runs that the engine/oil do not get warmed up. Water in the form of condensation gets in the oil and because the oil does not get hot enough, it doesn't get a chance to evaporate. This water will eventually deteriorate the oil's lubricant characteristics and durability.
- Don't believe the longevity claims (15k mi. or more). Chose the interval your manufacturer recommends, less if the conditions are challenging (I think this may be the heat cycles Mike is referring to). Personally I change oil every 5k mi.
- Don't forget hypoid oil for your diff. At least we don't have to worry about hypoid oil. But... I used to have a Subaru Forester MY 2007, manual, back when I was in Europe. At 20k kilometers
I decided to change the Subaru brand diff lubricant with the much revered Castrol Syntrax. To my horror, the supposedly viscous (90W IIR) Subaru hypoid oil ran out like black water!
I thought, well Castrol surely will not be like this. 20k km later, ...it was!
Like black water! From then on, I changed diff oil every 20 k km.
- Interestingly enough, he recommended buying gasoline from any premium brand. The reason was not the chance for off-spec gasoline, no batch of gasoline leaves the refinery off-spec. It was for the additives.
That is all my lunchtime lube oil education! For what it is worth...