I have seen buildup from Quaker State back in the 70's, not sure if they have changed things now or not. But I run Castrol in my 4 cyl, Valvoline in the 6&8's, Mobil 1 when I want Syn in a car, Amsoil in bikes, and Shell Rotala-T in Diesel's :D
If not for so many oil changes (about 120 qts a year) I would just use Mobile 1 or Amsoil. I have been having very good luck with Castrol in my 4cyl and the engine and ports are very clean that I am thinking about going stright Castrol except for the Diesel.
Charles