Я тоже, нашел:

However, even the brightest sun has its dark spots and GS's dark spot is that it seems they don't employ 316 steel which in fact is more or less standard. I don't know what kind of steel they use for their bracelet and case, but my impression is that the steel feels little softer than conventional 316 steel.
Seiko announced some while ago that they now will employ 316L steel for its Spring Drive line, and the reason that they didn't do it until now is that the 316 steel is harder to work with.

Взято отсюда:
http://www.watch-pop.com/seiko/answer-09946.html