If you have the tools and are comfortable working with static-sensitive devices you could try opening up the MnM and gently and carefully reseating all ribbon cables. That often fixes “flakey” digital synth problems.
Patience is required to gently remove all the screws, keep track of them, and put them back in place. Avoid carpet & synthetic clothing to keep the static down. If you have a friend who has successfully built a lot of PCs or repairs phones, offer them a six pack of their favorite beer or a few fancy espresso drinks and they may do it for you.
Edit: if you need help, let your friend know that the MnM is worth $3500 or so, and isn’t some weird old thrift store find.