Binko,
without buggering the slot?
A method I have used with stuck screws on the action of oldish Simsons is to grind a
proper turn screw blade that you can insert into your standing drill. Then fix the action
under the drill bit (no guys, he doesn't have to turn the drill on) and lower the bit
until you have the blade properly set into the screw head; then grab the bit and turn
it while you exert reasonable downward pressure with your other hand.
Did I explain myself? I don't know if this should work on the pivot pin screw, but at
least you won't bugger it. JMTC
JC