Start with checking for bad sockets in the gi circuit, common on old em's. The feature lighting sounds like a bad connection at a jones plug.

Check for loose fuse connections. These are all the easy process of elimination. From your description, as gi lights are working intermittently, that usually translates to a loose connection or bad socket.

That fuse holder will need replaced. It's weak and will give nothing but problems.

Did you definitely check all the Jones plugs? There's not too much else that would cause ALL of the controlled lamps to be out.

As dm said, about all that's left is a broken wire.

Wiggle the plugs for the controlled lights, plug and unplug a couple times, make sure they're not corroded. Also, I'm not sure if Gotts have a seperate fuse for contolled lights verses gi lights or not. If you found one bad fuse holder, good chance there's more. Don't just look at a fuse and assume it's good either, pull it and check it with a meter.