A continuation of my post above from a year ago.
After re-soldering the switch the lock worked for a few days then started failing occasionally and finally stopped working altogether.
I removed the tiny switch, disassembled it, then cleaned the contacts as described on page 1. Put it all back together but soldered wires to the contacts so if I had to remove the switch again it would take a few minutes and not 2 hours. Photo of the mess I created.
After about six months it again failed occasionally and finally stopped working.
Removed the black actuator case, checked out all the wiring, switches work as expected when testing from the plug pins (1-6).
Put it all back together and it worked!
Don't know what made the difference, perhaps a poor connection somewhere.
Maybe the actuator internal shaft somehow got into the wrong position and switch settings weren't as expected.
Having done all that I didn't want to stuff around forever with this so looked for a new actuator on ebay using search argument "Front Left or Right Door Lock Actuator for Holden Commodore VT VX VU VY VZ 99-05"
I bought one from gallop_autoparts in Sydney for $A38.80.
It does not have the rubber block on the side that the original does, and the plastic concertina dust cover doesn't quite extend to the full length of the shaft.
It was installed and has worked for a month now without problems.