Hermle units generally last 19 to as much as 30 years. We usually get calls to replace units that were built in the early 80's or late 70's. If you look at the back plate of the movement you will see a couple numbers above all the other numbers. You will see such as a 77 or an 83 or so on. This is the date the movement was built.
http://www.clockworks.com/hermle.html
Peccavi, July 2009