I've had all sorts of problems with my M401 passthroughs. I bought a bulk order of 10, and I only have two left. Seems that dripping / refilling the carts lets the liquid seep through the atomizer and shorts out (or clogs?)the microphone switch. I'm looking to mod one of the broken ones if I can get it apart without destroying the connector and put in a manual switch, then plugging the center hole to prevent seepage. Unfortunately, I get frustrated when working with these little gadgets (something to do with lack of nicotine) and I end up brute forcing them into non-existence (unless you count the pile of metal shavings and wires).