Hey Rob,

On the twist-sockets, bend the 2 small copper contacts bushes UPWARDS, so they make contact harder against the PCB when you screw them back in.
Looking at the side of the socket, you can slip a fine screwdriver under the contact, and then bend it upwards towards 45degress.
Works for me !!

I used to fix lotsa sign-displays (scores) at work that are full of those twist-lamps, and all the intermittent ones were fixed by simply bending the contacts UP as above......

MM.