Here's a couple of pics of the black XL clamp/heatsink on my buggy.
I have tried to file a flatspot on a motor before, and filed away for 10 mns and afterwards coudn't even tell where I had been fileing, maybe my file isnt good enough and I needed a diamond one (i do buy cheap tools against my dads advice) or maybe the Mega Motor I tried on has a harder shaft than Feagio, I didnt even try to file the flat on my Feagio, I just went straight in with the dremel after I taped up the motor and it turned out nicely.