I had the same problem on a 9L on my Rustler I pretty much did what BB8 suggested I never had to use heat, if you use heat apply only on the pinion and it should loosen up
If you can get the set screw from the pinion, run it without the set screw and the torque should get it loose.
Actually, I've been running it for a week or two without the set screw in. It's pretty well stuck on there. I'll try prying like a couple guys have suggested.