I guess it's a matter of whether you want to the little extra performance and engine protection...
When Slick 50 was the rage, I used it in all of my vehicles...
Believe it or not on 2 occasions it was proven to work...
(1) Lost oil pressure in my 1988 Mustang GT coming from my in-laws (my wife at the helm of course). Unfortunately, we didn't know it until we got caught in a really bad hailstorm about 30 miles north of Colorado Springs and had to stop.
A horrible sound was coming from the motor, and we cudn't get a tow truck, so we turned around a drove back to a dealer in the Springs. Their verdict was blown engine. To say I was pissed would be an understatement, and my wife volunteered to rebuild the motor herself...:smirk
Short version... The motor wasn't blown, the distributor shaft had broken and I cudn't find any other damage...
(2) Sent the head for my T-bird to have a major porting job done w/new rocker arms. The original set had 35,000 hard miles on them. Got a call from the guy doing the porting, cuz he had mixed up the new set with the old and cudn't tell which was which...:?:
Micrometer in-hand, I dashed down to see for myself, and cud never figure out which set was new vs. the old set...
Reg thanks again, I wasn't going to use Royal Purple in my motor this time around...but as they say "an ounce of prevention is worth a lb of cure."