Hi Rob,
Getting closer! I had another look at the schematic later on and have another couple of suggestions.

When you get a chance could you make a note of colour of the wires which run from the suspect 1C switch on the motor? The switches are identified by position /switch/ then wire colour. This might help locate it on the schematic and tell if it is related to these problems or not. I think the switch contacts are a bit worn and will need replacing but for the moment might be able to adjust the contacts.

Could you also try pressing the ball return switch on/off and watch what happens with the Q relay? The relay should follow the switch action and turn on/off but I suspect it was sticking on and not releasing properly. This relay controls whether the flipper or the ball shooter coil is activated by the right flipper button.

regards Derek