I have a M9P which was the last one Leica USA had in stock, exact time unknown. I have taken extremely good care of it and then I may have wet cleaned it one time with Eclipse , not positive but perhaps. Then the statement came from Leica that only non contact methods should be used because of the corrosion problem. A lens pen and lighted loupe were purchased and I used that if air blower did not clean sufficiently. I has always worked and is contact, but dry.
I still did not want to have to have a corroded sensor replaced specially now that the free program has ended, but the issue of humidity remained. My home is air conditioned although humidity is higher in summer and I take the camera outside. I could build a dry box, but incandescent bulbs to provide heat will become scarce.
All that said, I figured descant packs and sealed bag would do the trick. Internet searches were fruitless for small quantities. Last week I was on Amazon and used the search term silica descant and that was the key. You have to know the correct term. Lots of choices came up and I selected a 100 pack of 2 gram bags of rechargable packs, 2 is double what is come with lenses and cameras. Blue when new, pink when you need to place in oven to recharge and they turn back to blue. $10 or so is a small price to pay for protection in my opinion. Will see if it works.