I got an SL2 with a 50 Summilux for a fair amount more than the price you have been offered, and 1/2000 didn't work, and the prism was rather badly desilvered. Don Goldberg took care of both problems -- he has replacement prisms in stock. The work wasn't cheap.
I don't know whether the shutter issue is "universal" but it is a problem with the SL2 that is not present with the SL; don't know why. My understanding is that it WILL manifest itself at some point in the camera's life. Of course, SL2s are 30+ years old at this point, so I guess they're entitled.
Assuming you don't have either problem with your camera, or you can get it cured of those problems, I'd say go for it. It's a fine camera indeed! The shutter sound is a pleasing "whuff," which is much quieter than the rather sharp sound of the FM/FE Nikons. I assume the FM3A has a similar shutter sound to its older siblings; I've never tried one myself. I am a very big fan of the FM/FE and would love an FM3A. But if you've decided the Leica look is what you want, then there's only one way out!
I have gotten an SL to accompany the SL2 (which I like very much as well), and several 2-cam lenses since they're significantly cheaper than the 3-cam. Many of the 3-cam lenses are improved designs, optically or mechanically (for instance, regular size filter rings rather than those series filter sizes). However, I like the results I get from the 2-cammers. You may decide you want the 3-cam lenses, in which case you'd best be prepared to pay two or more times the cost of comparable Nikkors.