I found my 87 sube was starting to do strange things when it was 15 at 165k miles. never even had a valve cover off.
there is every smell of every type of petroleum product...
I took note, now on an 87 sube going on 23 years, also never taken apart. I have it setup to intentionally "smash" (there is a better word) all of the relief valves open, and let it hit the screen in the filter (a special filter, does not allow open bypass) by simply using 10w30 (heavy oil is not going to stop a trochoid oil pump- it forces relief valves). I have captured a perfect grease, stuff that you could find on a truck fifth wheel, I smell ether, and diesels depending on the weather, and it is all micronic layers, letting go, and gathering, and dispersing, no actual chemical to find, except for the grease looking stuff. And it is pure. The engine invented it.
If to wonder what happens in real longevity...it is some type of perfection, a distillery, it can all burn.
Then there is that unbreakable petroleum product. doesn't burn, doesn't lubricate, what is the name of that stuff.... ?