I used 470 ohm 1/2 watt resistors in a bally kings of steel worked perfect, I used pinball life 39 cent leds, some I had to turn 180 for them to light, but all worked, just strobed so after adding the resistors they all worked as they should.

Probably the socket, I read there are two different style sockets, and some people were having problems with certain leds I games, check sockets for corrosion, check the bottom of socket where the end of bulb gets contact. Regular incadecent bulbs work?