These discussions are good, sharing thoughts and experiences.
Like points vs electronic ignitions.
Oil threads a must.
I recently added an oil with known high doses of zinc and phosphorus into the oil I have recently filled at last oil change.
Shifting is much smoother.
I have mixed the oils before, last time the more modern oil only as a test. A synthetic, not the more expensive ester synth. All of same viscosity.
It does not have all the lubrication additives as my bike needs, probably catalytic converter friendly modern oil .
I did not add much oil with high doses of zinc etc, 1/2 litre made a difference.