colas said..
No, the steam-in-the-shower is a myth.

The damage comes (on the long term) from the temperature changes, by contraction/expansion of the pieces and joint, and promoting local (tiny) condensation in some places inside the watch on cooling.

Granted, this also happen in normal use by getting in and out cold water during sessions, there is just no need to also add stress by hot showers.

This is similar on why you do not let dry a wetsuit in the sun, even hough they are exposed to the sun while SUPing.