I planned on drilling my mirror mounts as soon as my 2012 was delivered after reading all the threads about it. But then my son drilled the mounts on his 2010 JKU right after washing it, and no water at all came out.
I checked my 2012 and found that the tiny weep-holes at the bottom of each mount seem to be open. I can stick a fine broom-corn up in it freely. I got the impression that something was closing off this weep-hole, and that's why drilling worked.
I now plan on waiting at least well into our wet winter and periodically check/clean the weep-holes and see if I have a problem.