Is it definately A.C driving the motor?

Sorry, i can't see whee the voltages come from, beyond that 4-pin connector on the left side of schematic....

To me, it looks like a typical DC driven motor-switching arrangement, the electro's probably used for de-glitching the relay contacts during changeover etc...

You might find 1 cap is open, or even low impedance causing your 'shuddering' problem.

Anyway, changing the caps is a good start, easier than finding that motor :-)
A modern .01uf 630v greencap will be fine.

MM.