I've been keeping a rather close eye on the global SR-Ω market for 8 years now and I can safely say that very few units have had the drivers replaced, quite a bit less than 5% of the 600 or so units made. As for there being some design failure that will cause all units to be fubar at some time is just utter BS. Stax did change the cartwheel design to etched aluminum but only once production had ceased. The cartwheel is the most fragile part of the driver so if a violent shock breaks or even distorts it slightly then the drivers are toast. Makes sense to strengthen that part but the resin version is by no means defective.
What we have to look at is the reason why Stax swaps out drivers. Channel imbalance being the main reason but they never look into what's causing it, they just scrap the drivers on the spot and use what ever current replacements they may have. Most of the time the channel imbalance is just temporary and will go away with use or just a change in the weather. Now a tiny amount of drivers have suffered permanent damage due to arcing or from amps where the builder didn't know how to do bias supplies, i.e. Ciuffoli and Rudistor.