Piston Seal. Poor thing, should be ashamed of yourself! Yes I have used that product successfully. I think it really only works on low compression cars as it is a botch that wears off over time. A recognised tool of the dodgy motor seller. I used it to get rid of a Mini.
STP and its chums. Particularly good advertising and by association to winning and trendy peeps. Really it was an additive before the oil companies offered technically advanced lubricants. The selling ploy for dodgy gearbox was to wind ladies stockings into them. Used to take the play up well for a bit.
Flexi pipe on A series transverse. An attractive botch which did not solve a rocking engine. The dodge was to insert a bit of well fitting pipe into the exhaust end and up into the manifold and put the clamp on the flared joint. This would not move. If it did then attaching a further tie rod to the head onto the front of the car stopped it rocking on the mountings. By that time you might well have got rid of the poor manifold and clamp which was worth an extra 2 or 3 hp plus a better exhaust connection. Nothing wrong with the SU carb though.
Redex, never really had much to do with that but we are back to before oil companies put much in the way of additives in there products. Got a Redex injector, nice.
Colourtune, again never used one. Always favoured the Italian tune up of belting down the road after adjustment. The fastest setting would be 'tuned' right. Thus ultimately ended up with a Mini on twin Reece Fish that could spin its wheels in any gear and used about a gallon of fuel every 15 miles until it found the offside ditch about 50 yards beyond a well known corner on the downs at 2 o'clock in the morning. I had to sell the wreckage and good bits for a replacement car to get to work despite impressing my buds with an impressive performance. Would not say it was the last silly thing I did in a car but the cost of being an arse was well and truly learned and not repeated. Colourtune could have changed my life and I might be a mild mannered civil servant somewhere.
I raise you - Sparkrite electronic ignition, used the contacts and rode piggyback on the coil increasing the energy of the HT charge while not burning out the points. Even had a switch to turn it off. Yes, folks, it might decide not to work. Trabbi versions do not have a switch to turn them off and had a habit of melting. Ideal for a Schmitt or other single stroker really, unless you have two for your twin. Did that to my Goggo. Went well until it did not goggo at all. No Goggo likes a smartarse! It was that fav rave of the Goggo, holes in the top of the piston, burned through by the heat of the pre-combustion prior to the flame front converting the charge. This despite timing being bang correct. Goggos are rather sensitive to this so always have them timed up well.