OK well finally back with a report of success with the Drive B encoder. Did the connection reversal for pins A and B of the encoder (1 and 3 on the PCB diagram from the service manual). No need to cut the tracks as both solder ring pads had been lost but I still had to undo the track repair. Also, in the process of de-soldering the encoder for the nth time, the solder pad for pin 4 also came off, so had to make a new bridge connection for that.
Another figure of the rather messy repair: hairs on the area were from cotton buds during cleanup. Pink stuff is nail varnish remaining from the earlier track repair.
Anyway after covering the area with Kapton tape and reassembling the rewired PCB back into the front panel, all functions of the encoder were exactly as anticipated (clockwise + counter clockwise) and the push-button switch works fine. Earlier worries about the amount of force needed to push the switch were allayed and it is not so forceful as to move the whole deck.
With the above success I revisited the left-sided encoder (Drive A) of the W1 and rewired it according to the principle above, which is a much more solid repair as all the legs can be soldered to the board and the bridge wires added. It's a different wiring layout, which I can include in a repair section of the MD Wiki as requested.
Thanks everyone, especially of course @kgallen for all the advice.