I have found a cure for MCS...and it's carefully selecting which clarinets you buy, and doing much less experimenting with unusual or untested brands.
For example, I have had great luck with Selmer Paris instruments, and they can often be found for a great price in good repair. Additionally, many Couesnon and Thibouville clarinets (and their stencils) are also of very high quality -- I learned to identify their keywork and other markings, and try to stick to those (noting that resale on them will be substantially lower than instruments marked "Buffet" or "Selmer Paris"). But, following these simple rules, I find that I buy fewer clarinets, and those that I buy are of substantially higher quality to begin with. Thus, fewer mediocre clarinets.
Note that Phil's Clarinetpages.net website is a terrific resource. And also note that you may prefer other brands names. Just laying out my experiences for my type of playing.
Also, as a side benefit, I find that having better instruments also leads me to want to play them more. Thus, my time is spent practicing and improving my skills as a clarinet player and musician rather than tinkering and flea marketing. I'm finding it much more satisfying and relaxing....again, your mileage may vary....