Thanks guys, have followed your suggestions. I also replaced another dead holder that only has one wire and a braid. Both failed. I decided to reflow the solder on the offending pins on the lamp driver, no go

I tried checking the scr's but unsure if I did it right. I put the dmm on diode/beep and touched the two outside legs and got a beep on known working globes and the dead ones. No beep when touching the middle leg and the outside ones

Please confirm if this is correct?

I did investigate the connectors inside the plugs and they all seem quite tarnished. So if what I did above was ok, it would seem a session of replacing connectors is required. Doing this is the most time consuming for me and why I have left this to last.