Stuck rear mech pivot bolt

[eck]

When I tried to get the rear wheel out, I couldn't pivot the mech back out  of the way, as you would normally do. The bolt holding the rear mech in the threaded hanger is seized, not in the hanger, but it seems to be seized in the mech itself: it can turn a little, < a quarter turn, in the hanger, but the mech turns with it.  I'm in danger of rounding the allen bolt if I apply any more force.

I've skooshed the whole ensemble with Magic Spray ^TM. and will revisit it in the morning. Meanwhile, any ideas for getting the bolt out? 
Thanks

[rae]

Work it backwards and forwards to get oil in the thread.  Failing that, violence.  The traditional method (heat) is ruled out due to frame/paint issues.

The allen socket in most mechs is quite deep and takes quite a bit of torque.   Use a decent hardened steel key - the cheap ones round off and damage your bolts.

[rogerzilla]

The local fastener shop recommend brake fluid as the ultimate thread freeing substance.  OK if the mech isn't painted.

[eck]

Work it backwards and forwards to get oil in the thread.  Failing that, violence.  The traditional method (heat) is ruled out due to frame/paint issues.

The allen socket in most mechs is quite deep and takes quite a bit of torque.   Use a decent hardened steel key - the cheap ones round off and damage your bolts.

Violence  - works every time. 

I had to resort to cutting off the wee tag that butts on to the lug on the hanger. Then I just turned the whole thing off by hand. Somehow the pivot bolt has seized in the mech.