Slick 50 an additive from the past .

If I remember correctly Slick 50 and STP were really thick and it was that which quietened noisy tappers or even rumbling crankshafts plus many other things. It was commonplace for sellers to put those oils in engines to hide nasty unwanted noises.
But they blocked oilways in some engines. Fords Pinto engine had poor oil feed to the overhead camshaft which resulted in a loud ticking noise ... Folk added those oils to quieten the tick but it was short lived as the ticking got really loud and the camshaft had to be changed.

Quality modern oils don’t need additives ..

Slick 50 was a thin light coloured liquid and was only promoted as adding extra protection to the engine, unlike Wynns and other brands that Supposedly fixed problems like  ..stop smoke, reduce gearbox of diff whine and expanded old oil seal but I always dismissed them !

That’s sounds very old school😉 ...another favourite of the time was saw dust in the diff to keep it quite to sell 🙄

I used slick 50 in my old mk1 cavaliers it was at the time a great product the beauty of it was unlike wynns and stp it was a once only treatment rather than an additive at each oil change, it did seem to make a difference to those engines of course the big selling point was that it would protect the engine even if it ran out of oil and those old cars did like to use a bit or leak it out!!! I'm not sure if it would help our modern engines im no engineer but surely it cant hurt as others have said it wasnt thick glutinous stuff maybe ill give it a try in my Rav and report to you all😁

I wouldn’t use it especially with todays DPFs and EGRs….. More so if the engine burns any oil even if only a little…. 
The 0 grade oil I use in the RAV4 is so thin it’s unbelievable… Gone are the days of oils with treacle added to mask noises… 

A guy I had the pleasure to know when I was young, served his apprenticeship with Rolls Royce, worked for many years for Aston Martin, finaly worked for Bristol cars and for the latter years ran the Bristol racing team, back in the days when they used to drive the cars down to Le Mans, then spend a week trying to tune the cars to the local fuel.

Anyway when at Bristol they did extensive tests on all the engine additives available at that time, the only one that was really benificial was Bardahl

www.bardahl.nl/en/Products/Additive-advice/

But this information information is about 60-70 years out of date🤣

The guy i knew was also a keen hifi enthusiast, i was an apprentice working for acsmall hifi manufacturer and Percy used to come in from time to time to make prototype metalwork for us, so I got to know him a bit, my older brother had known him for years and had plenty of stories about him.

The one i know, was about the car he had when I knew him, which was a Citroën GSA that he had from new. He was never happy about the smoothness of the engine, which was a 1300 air cooled flat four, which tend to be very smooth runners, after several times of being dismissed by the dealer service department, he removed and stripped the engine down (bear in mind he was in his 70s at this point), he discovered what the problem was, the pistons had slightly offset gudgen pins, and one of the pistons had been installed the wrong way round, at the same time he studded the design of the piston and had ideas on how it could be improved. He wrote to Citroën explaining his ideas, he got a polite thanks but no thanks short reply.

Rather than give up, he wrote again, but this time on his old Bristol Racing Team headed note paper, signing himself as ex head of the Bristol Motor racing team. This time he heard nothing for about 6 months, then a box arrived with 4 pistons with changes as per his recommendations, this time with a nice covering letter thanking him for his input, and in fact they agreed that there were definitely some improvements with this design but at this stage they would not be implemented in production, I think they probably gave it to an apprentice as a project, but it is interesting what a bit of headed note paper and signing it the right way can pull some weight.