Werner
Welcome to the club and what a great watch to start your Heuer journey. These are certainly not seen in abundance and like all Carrera's of the period they were never made in large numbers (compared to Rolex) so they are all scarce. This one probably no more so then any of the other scale dial executions and you will wait a long tome before another one comes available. The condition is however outstanding and as a seasoned collector I am sure you appreciate that as much as anything. Strangely enough or by some coincidence there was one German eBay just the other day. The auction was stopped before the end so one can surmise that the seller was made an offer he/she could not refuse.

Accurately dating any vintage Heuer is all but impossible so my guess would be around 1966 to 1968 based on a 700xx serial number. Mr Moss may have more to add here.
Cannot help with sourcing a new crystal but they also come up on eBay from time to time.

Its a great addition to any collection.
regards
Paul
www.heuerworld.com