I have read this thread with interest and all I have gained is a lot of confusion. I have used STP in my cars for the past 20 years and any engine I have had worked on or torn down has been very clean. This is not an endorsement of STP nor to start an argument about it. As for the various oils, go to any dealer here and they will all tell you their brand has everything needed for any application. I suppose if you poured to much STP in it could leave deposits, but I always run my engines until the
oil is hot and then with the engine running I put in about a half can and then go drive it again to make sure it is well mixed with the
oil.
Ron