From my personal experience, I'd say that there isn't a relation between the age of Minox 35 cameras and their reliability. The ultra compact 35 concept is so attractive that I really, really wanted one, and I tried three (!) before I finally gave up..
I've had two GT-E's, new, both plagued by intermittently failing shutters. I've also had an older MB. The MB's shutter was fine, but the lens had problems under some circumstances; in daylight it would flare like madness, even with the Minox lens hood mounted and the sun from behind.. possibly a case of lens separation. When the ISO dial on the botton started to fail, I tossed it.. No more Minox 35s for me, it's just not worth the trouble.
I'm now shooting with an XA2, and couldn't be happier. It just works! Always. Never misses a shot and doesn't flare.
If you've had a couple of Minox 35 over the last years, you should really think about why you didn't hold on to them. I see in your sig that you have an XA2 too. If you have and it works.. my advice would be not to bother with a Minox 35..