I believe the socket you are looking for is prewar part 138-21. Frequently Lionel uses a fiber washer with a small eyelet crimped in it inside the brass socked shell. There is a wire soldered to the brass eyelet. The brass eyelet acts as the center contact that contacts the center of the lamp. A short in the socked is probably due to the wire touching the shell. This is sometime caused by years of pressure from the tightened lamp distorting the fiber washer. The problem can be corrected by replacing the wire and fiber washer. The fiber washer with the eyelet is part 61-22. I do not know where to get the lamp socket 138-21, however I believe it was reproduced by MTH. The washer 61-22 is available from most part dealers.