Why are there still people who believe that Quaker State and Pennzoil motor oils contain parraffin wax? All modern conventional motor oils are parraffinic according to what I have been able to find out. And that is not the same as the oil containing wax. I don't believe that QS and Pennzoil even get much if any of their oil from from Penn oil fields anymore. There is still oil in those fields but those fields became unproductive a long time ago. Pennzoil might be using oil from Texas, Oklahoma, or the Middle East for as much as we know.
Just because Slick 50 is still being sold from Shell/Pennzoil/Quaker State does not mean the there is something wrong with Shell, Pennzoil, or Quaker State motor oil. If there was something seriously wrong with Pennzoil oil we would know about it pretty soon since Pennzoil still sells a lot of oil.
I would not buy Slick 50 myself and put it in my engine. But I can buy Pennzoil oil and use it without having to buy Slick 50.
I do dislike a lot of the disceptive motor oil advertising. All quality motor oils contain detergent/disperant additives and when somebody starts bragging about their anti-sludge formula I start to become turned off by that sort of advertising. Do you know what causes sludge? People not changing their oil frequently enough, people letting their motor oil levels get low in their car or truck engines, and people using poor quality motor oil. And there have been a few sludge prone engines. If a person changes their motor oil frequently enough and uses a good quality motor oil, then that person will probably not have a lot of sludge in their engine regardless if they are using Valvoline, Pennzoil, Quaker State, Castrol, Chevron, Halvoline, or whatever. Contrary to the advertising you don't have to use a certain brand of oil to avoid sludge in your engine.
If you really want to reduce sludge buildup in your engine use maintenance doses of Auto-RX.
I personally like to use conventional motor oil most of the year because I like to do reasonable oil change intervals. I am willing to use various brands of conventional motor oil-Chevron, Pennzoil, Halvoline are all good. For the winter months I like to use a synthetic oil since there is no getting around the fact that a synthetic oil will flow better in the cold. And I like to use Auto-RX to keep my engine clean. No Slick 50 for me. I am proud I never used that stuff. But I have to admit that a long time ago I was taken in by another PTFE containing oil supplement.