I have had twp M7's for about 4 years now.
About a year ago after both being sent to Solm's for upgrades, I had the reported jam on one. It was sent, actually Leica NJ sent UPS to pick it up and was back within a week. No problems since then.
If I was using an M7 as a Professional, I would ALWAYS have another M body with me. When I did weddings with the M7's, I always had two with me.
As an amateur these days, I can afford to only take along one M7.
But if only using one M and if I was going where I could not get service readily for an extended period of time and required as close to 100% reliability as I could obtain, I would get a Mint M6 or Mint MP.
As of this date, I have not heard from Leica or any other M7 user exactly what is causing these jams and a way to clear them without sending the camera in for service.-Dick