Well, I was able to open my B2 after few tries with a small screwdriver. It was very well sealed inside and completely dry, so the sweat being the cause of the damage is very unlikely. My UM3X was completely taken by water inside. The B2 is perfect, like new, so I believe both stopping working in the same week was just an unfortunate coincidence.
Or the reason is another, like the constant hard steps over and over, but I really don't believe that. Anyway, the BAs seem to be damaged since I put it to play while open and it still distorts all the time. Left unit is perfect.
Now I need to open my left side UM3X taken by sweat. Wish me luck. =D