Its amazing how good it is to leave something and come back with a fresh mind....

As said above, i found the voltage of the opto collector for Sw32 had no (or minimal) voltage.  I then determined that it was the red/orange wire that was the problem, (as the other grey wire had power when tested in conjunction with another switch beside it).

There was continuity to the connector on the 16 opto PCB.

This trace then went to a resistor.....and.....it read WAY higher than all the others, there was also a mark down the length of it.

Looking at the circuit diagram, it was a 2k resistor, i found a 2.2k one in the shed, put it in and everything worked sweet .

Thanks to all who helped, particularly those who suggested checking all switches that store balls under the playfield.

Only other question is will it be an issue with a slightly larger resistor?  I assume not as the others all seem to have a bit of variation.