Well, the KVAFM is an optical metering system. While it's sealed to prevent damage some moisture seeping in can fog the optics and render the sensor useless... It would take a lot to soak it to the point that the temp sensor would degrade beyond providing any signal though.
So did you actually try your friend's AFM in your car?
Well I tested the green and red wire and it was bad (the one that the safc2)