Do not put a new assembly in your machine, the problem is not mechanical.
You Clearly don’t have enough power in your hold circuit. It could be the coil or it could be the driver board that sendS the reduced power in the hold (after the eos is triggered. )
If you jumper the EOS together or adjust so it doesn’t open, you should have plenty of hold power. Don’t do it long as it will burn the coil of course. This will prove you you that the mechanics aren’t the problem if you don’t believe it.
It’s prob not the coils as these are single windings but you could Swap the coils side to side. If the problem moves, it’s the coil, if not it’s the hold circuit.
You could also measure the power sent to the coil when the EOS is activated to see if there is a difference between the sides.
I don’t know the spike system enough to help track Down the circuit. As suggested, call chas at stern to help before you throw parts at it.