I find myself in a similar position with my M4, which I've owned for about 13 years now. It's an early one, probably built in December 1966 from the first batch. I bought it along with a CLA'd DR Summicron from Sherry Krauter, which dates from 1957. I displayed the Leica far more than using it although it was in fine shape. However, just this past week, while I was out an about with it, the film advance suddenly stopped working and the cause turned out being the shutter curtain separating. Both DAG and YYe told me the M4 only crimped, not crimped and glued like earlier Ms. No matter who I send it to, it's going to end up being $600-700 (would replace lugs while at it) and my dilemma is, I simply don't use it much compared to my Fuji XE3, XP1, and XT1. But I've got 21 rolls of film in the freezer (all assorted B&W)! I ended up paying about $600 for this camera after a small price adjustment for something undisclosed from Samy's ebay sales. So now, I'll be into the camera $1200-1300 with a CLA, shutter curtain repair/replacement, and new lugs. I could sell it off as is and make a profit or fix it and keep it even if it gets light use and I'm getting on in years (and my kids just use their phones - to them, my cameras are an anachronism). FWIW, I'm sending the M4 off to DAG next week. I hope he's the Leica shaman people say.