Lionel 154 crossing signals repair help

Hi,   I'm trying to repair a 154 crossing signal and have some questions re: the disassembly. A friend gave me two of these signals - one with black cross arms and the non functioning one has white cross arms.  Looking at Lionel's support manual, these signals had a printed circuit board in them.  Is that correct or do I have older models which didn't use electronics to control the flashing of both lights?  Speaking of lights, the manual says these bulbs simply pull out.  Guess they are like the old style Christmas tree lamps that had power contact strips on both sides of the lamp base.  With the black shield over the top of the lamp, I'm a little nervous trying to pry the bulbs out if they're corroded in place.  Can I simply straighten/loosen the four metal tabs under the base and will this free up the mast?  This signal does not have screws securing the white cross arms or the black lamp fixture.  Not sure but they might be plastic. I used a DVM to check continuity of the lamps but no measure between any of the three contacts.  All I did get (using the highest resistance setting of 20M ohm) was an initial reading of 17 rapidly decreasing to 3.  Like it was reading across a capacitor.  Thanks for any help you can give me.     Bob