I shoot an EC, it has electronic shutter timings whereas the S2a is all mechanical, besides that I don't think there is much difference between them.
The S2, S2a and EC are oooold cameras now so you have to assume there will be light seal and foam degradation problems
I've heard the S2a had parts made from some slightly less durable materials than the S2 and EC, some talk of gear failure but I can't provide any evidence to support this.
Whichever camera of the three you choose, if it goes belly up, repair is an unlikely option considering their age and the availability of parts.
Having said that, they were built to last, tough as old boots.
Flash sync is 1/40th because its a focal plane shutter if that matters, but there is a leaf shutter lens or two amongst what is a large and fairly available range.
Another minor negative on the S2 & S2a is the full size mirror flapping about in there every actuation, its like a shotgun going off and produces some vibration, easily remedied with mirror lock-up....if you remember that is.
That's about it for negs, they are reliable quality cameras with a comprehensive range of quality lenses, they're just getting a bit long in the tooth, a late S2a is gonna be 40+ years old.
I only know one person here with an S2a, photostar, she may be able to tell you more about it..
