[Leica] M3 body / film curtain

["John Hudson" <jahudson@direct.ca>]

I have a single wind M3 body s/n 101xxxx owned continuously since 1965 and
which had a thorough overhaul, cleaning, lubrication, and recalibration back
to specs in June 1998 at Kindermann Canada.

Today for the first time ever to my knowledge the film curtain stuck open.
With a new reel of film the first  five shutter releases worked just fine.
On the sixth shot the curtain opened and remained open. The film winder
lever will not move and the delayed timer mechanism will not trip the
curtain back to the closed position. The camera has not been subject to any
physical abuse or mistreatment.

Are there any suggestions as to what might be ailing my M3 body and what
might I expect as regards the diagnosis and the cost of repair?

John Hudson