Curtis, I'm with you about 98% - Except when it comes to oil additives.. Some of the (such as STP et al), have Zinc in them which flat tappet engines in particular really need. The EPA has legislated zinc out of all automotive and light truck oils. I believe there is still some level of zinc in the oils made for heavy trucks - which most of us use in our diesels. Aircraft oil also seems to have escaped the ax.

Regarding Slick-50 -- that was some pretty odd stuff.. I used it for a while and never saw any difference in power or temps on the dyno.. The ODD part of it was that the FAA actually certified it for use in turboprop propeller gear boxes.. It also got a mil-spec as I recall..