just to give you a little backgrounder, aeg7757.. i am all for using oil additive, and my favorite is the Lucas oil stabilizer, i have tried it on all of my toys, boat, scooter, motorcycles, and also my lawn mower, and it did work great, it silence the noisy engine dramatically.
although when i used it on my mini, i noticed the oil pressure went down a bit when engine is hot. and then i asked myself, with all the article going around the if the oil pressure goes down when engine is hot, it means that your bearings are shot., well, for a while i got hopeless, but then, when i change my oil to pure 20w50(no lucas this time), the oil pressure goes up. it goes to show that the oil pressure goes down when hot because the oil thins out when hot, although it's still protected with teflon which is the main component of the Lucas oil stabilizer. So in the morning when you start your car, the sidewall of the engine block is protected with thin film of teflon.
And also the oil brand Quaker(green bottle) is i guess the best there is, i saw this video where in two metal bars is made to rub onto each other mechanically while being soaked in oil, different oil were tested, it takes days before you see some evident scar on the metal bars due to friction,  the Quaker, took weeks and only shim of tiny tiny scar was seen in the point of friction.

Around here, we are just as concerned about wasting rare (and getting rarer) Mini engines and transmissions. Additives can be drained and replaced if they don't work.  Mini engines.... not so much.

Engine oil mostly provides a thin layer of lube to prevent clean engine surfaces (e.g. bearing faces, rings etc.) sliding or rolling smoothly without making metal to metal contact in high temperature areas with added engine by-pass chemistry mixed in. It is thinner to get pumped in, where the oil pressure keeps the right spaces.

Transmission oil has the job of being compressed and ground between gear teeth as well as trying to prevent friction between metal surfaces under higher pressure, but without the chemical contaminants and extreme temperatures. There is no oil pump, so the oil is thick enough to do the job (e.g 90 weight in differentials).

In a Mini engine the oil has to do both jobs, pumpable to get into the crankshaft bearings etc. and withstand heat and chemical attack, yet be thick enough to hold gear differential teeth apart as well as protect the cam from solid camshaft lifters etc.

You can try to find an additive that does all that, but dollars-to-donuts one additive will do one thing, another will do another, but they will fight each other.

Ok but if money was no problem has anyone tried it?

Using an additive is a waste of $ IMO because you need to change the oil in a Mini often because it gets beat-up in in the transmission unlike most cars.

This goes along with the oil question that was posted.  Their are pro's and con's about this but here's my take what's your's I use valvoline 
20/50 racing oil in 1967 cooper  S now I don't have to add zinc factory says it has it in. Has anyone used an additive like prolong? 
for years I use prolong booster every oil change in my vehicle's and have had no problems over 260,000 miles on one vehicle and none of my vehicle's use one drop of oil between oil changes. Have not used in a classic mini cooper has any one? I no the wear factor in a classic if reduced would be a great advantage let's here from everybody and see there opinion.