Hmm. Nope, I've not ever destroyed a tank with an MG. Not every really tried. I have however used a jeep with great effect vs an M3, M8, and M18.
Many people forget that once the turret is out on the M8 and M18 it has no armament at all (ditto for the Firefly). With the .50 cal HMG on the jeep, I've destroyed M3's and M8's, and turreted M18's and Wirby's.