Think about SM58s that I've found is that the old ones seem to be built better than the newer ones. Last one I had had so much handling noise I found it almost unusable. I tried another one and it was the same. They didn't use to be like that.
Yes, we have several old SM-58's in the studio, and I'm glad we held on to them as the newer ones (not just Shure, by the way) might be less reliable.
I suspect some of it may be due to the type of solder used in newer products.
We had one client arrive with his brand new SM-58 and he was forced to use one of our older back-ups because of noise issues.
Hopefully, this was an isolated incident, as this could be very disappointing...an SM-58 was pretty much a sure bet if one needed a good microphone.
Ian