Bayonet sockets can be a pain in almost any era pin. Here's what I do with them if they are accessible before I replace them"

1. Clean inside with alcohol
2. Clean with dremel focusing on the inside near the lock channels and the cup on the end of the spring
3. Clean again with alcohol
4. Grab cup on end of spring with pliers or hemostat and pull toward end of socket. It won't move much
5. Use pliers to pinch in the free tabs on the lock channel a bit. Too much and the bulb wont go in.

This refurbs the socket. If it doesn't work after this there are a couple other tricks on pinwiki but it probably needs to be replaced