Stewart I solved this (after doing an unsuccessful clean up) by going inside the wing and pushing the wiring forward, having made a good contact I then put a dab of silicone to stop the wiring vibrating back out. its a pressure thing as well as a corroded contact.
Ideally a new lamp with a decent spring is the real answer.
Good Idea on the silicone behind to stop the wire to the central pin pulling out further from the back
I think the main cause of this issue is the rubbish card isolating washer
If it was something more substantial that had the central pin glued into its centre, there wouldn’t be a problem
