Just to share, I went through this on my 69 last year.
Should start out with a good socket. If the dome assembly is out of the car, you can try cleaning with vinegar and baking soda solution. Either soak it or brush it with a tooth brush. Then rinse clean and dry it. It should eliminate that corrosion and the socket will be bright colored again.
Also the bottom of the socket should have a bit of spring to it, that helps w the bulb connection, if not, work it or replace the socket.
Get your new bulb, lightly coat it w dielectric grease, (Vaseline will do). If all is clean, it will twist in easily.
Stands to reason your dome light was working and just suddenly stopped, that was exactly what happened to mine.
