How to clean loctal tube sockets?

[cbenham]

The Philco set in my avatar has several loctal tubes that cause interruptions in the picture and crashing noises in the sound.

I've cleaned the tube pins, cleaned the socket contacts, tried NOS replacement tubes, checked for cold solder joints and wires that were never soldered in 1950 on the sockets.

The top of the sockets have a light colored cover that I've never tried to remove for fear of doing irreparable damage to them.

Anyone know some good tricks to making these 60+ year old sockets reliable again?

Thanks for any help.

Cliff