The M9 was mentioned upthread. That has an traditional slow cloth shutter so should be good for several hundred thousand actuations (the M3 is said to be good for 500,000). What this figure actually means is unclear; probably the life of the curtains, although an electronically-timed shutter may well hold its tolerances for most of that period. A mechanical M is unlikely to maintain correct speeds for 500,000 actuations unless they are shot within a couple of years, although it will only need adjusting to bring it back within spec, not new parts.