Sealed ball joints are a great invention for sure buy I have not found the need in nearly 40 years of mini driving and I clock up a decent mileage in my daily driver that hasn`t needed any adjustment in a few years so for a car that`s used for sunny days I really don`t see the point.
A grease gun is also a great invention I guess
Yes, fitted new ball-joints when I first got my mini, 35,000 miles later they seem to be in good nick still. A squirt of grease every few thousand miles does wonders.