I use no additives in my motor oil. Used to use STP 40 or more years ago, but with modern oils I feel they do the job with out any thing else.

 

STP was bad 40 years ago too, but not Rislone or even MMO.

 

The only ones that I knew that a problem with STP were the ones that didn't follow the directions to pour it in after the oil was warmed up to operating temperature while running and then drive it for a short while. I used it for several years on my cars and dirt track cars with zero problems.