Adding too skeets sugestion , i had the same problem today with an etek i was teching .
If you have a strong enough grip without using a vice then hold the body tight with the allen key in place and hit it sharply with a wooden mallet.
A couple of sharp taps later and no damage it was undone.
When putting it back together place a dab of dye or shocker lube on the threads and areas where it is metal on metal or i should say alloy on alloy.
This tends to aid your next service.
Carl