What oil?
Just curious.
How many years is a few?
My civic story at at least ten.
In other words were they "newer" engines.
And was either or both of the engines injected.
I'm sure there are a variables.
How much ring blowby.
Temperature is a big factor as I recall.
Does the valve cover stay hot or cold?
I think that might cause the deposits we see.
And is the engine operating temperature a factor?
We know new engines run hotter.
And of course, syn just MAY cause less deposits.
Certainly plausible.
I'm running it now in my 86 318 with a Q-Jet. My rocker's sure look clean through the hole.