I have an Omega *real* analog auto-wind (no battery) from the early
sixties
that still runs like a swiss clock (cough!). It has a "one-piece-case"
i.e. no
rear access -- probably part of the 100m immersion rating. It needs a
special
tool which apparently flexes the glass/perspec/acrylic front to remove it.

If it's a "good" watch, it has a mineral cover, not plastic. Some watches
have undoped sapphire (aluminum oxide) covers.