Do you have one of the newer ones with the switching BEC in it? If you do, the external BEC shouldnt matter.
Check to see that the heatsink scews are tight. I read somewhere in another forum that somebody was having issues with this and their heatsink screws were loose and it effected the cooling.
Also check that you didnt blow a capacitior. That could cause it tor run hot as well.
I can't decide if its more fun
to make it...
or break it...
When i've recieve my MGM from RCM, 3 of the 8 screw that hold the head sink was loose.
I've remove all 8 screws and place a little , very little amount of blue locktite on each screw.
And for the BEC, i've the new version with the internal switching BEC but i run it with an external CCBEC.