This will make you want to use a low saps oil!
But will that eliminate the problem? I'm not so sure...
Great question. I suspect its caused by higher saps levels, based on some engineering statements made over the years. You're right we can't be sure.
It is speculated that Valvoline is putting some of its patented "Valvoline Premium Blue Restore" low aniline point oil patented chemicals in Valvoline Modern Engine oil. Although their Restore product mostly affects the ringlands on engines.https://www.bobistheoilguy.com/foru...arbon-cleaning-valvoline-premium-restore
It dissolves carbon: https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4995896/1
Several years ago Lubrizol thought valve deposits in DI engines were at least partly caused by ash combined with carbon, getting sticky. I'm not sure if they were ever right about it. They might be.
Too bad weren't shown a TGDI camera-shot, having 40-50K and using Modern Engine exclusively.
That would make it correct for sure. Maybe every 5 years we should run Valvoline Premium Blue Restore oil through the engine and see if that helps. Some would circulate via the PCV into the intake presumably from oil mist. Enough to do something up there.