Tom wrote:
On anything but the thinnest twigs, the old hedge clipper will bind
and I'll hear that loud squealing noise. I took it apart and inside
there is a rotating wheel with sort of splines on it, which is driven
by the motor. This presses into a sort of cylinder and the friction
fit drives the cylinder, which works the clipper teeth. It's old and
worn, so it slips and squeals.

Is there any way to repair it to get another season or two out of it?
Thanks.

Lube it regularly, both the gears and the blade, is the best suggestion I can
make. You might be able to replace the gears, then do that.