Frozen Setscrews

[Ron Evans]

HELP!

Five simple plastic knobs on a Hallicrafters SX-130.  Held to their
shafts with a slotted setscrew (not allen head).

Despite my best efforts, I can't budge a one of them.

I've dropped lightweight lubricating oil in the holes, let it set for a
half hour or so, repeated, and then tried to break the frozen little
devils free.
Clamped my channel locks onto my precision screwdriver and STILL
couldn't break a single setscrew free.  Grrrrrrrrrrr!

I don't know if there's a metal insert in the knobs or not...may just be
the setscrew in the plastic threads of the knobs.  I've never had this
problem before EVER!  'Bout at the end of my rope.

Surely others have also faced this problem.  Any solutions that have
worked well?

Thanks in advance!

Ron - K5MVR