This post is actually by PilotLight also: [link=http://www.rcuniverse.com/forum/fb.asp?m=5806547]link[/link]. The aluminum is soft enough that you can just use a rounded filer and file until you completely uncover the slit in the motor (on both sides). Others have also resorted to just cutting off a square pieces from the heatsink, starting at the level above the motor slits.