My guess is the juice is the culprit. I use my RM2 all day, everyday. But I used unflavored nic,so even after months of continous use, I have no buildup.
Same deal in my wife's woodvil, and my son's grand.
ETA: I vape unflavored nic that I get for around $45 per liter (at 24mg). Even
vaping at 24mg, that works out to about $1.35 for 30ml (if my math can be trusted this late at night).