terminator 2 arcade gun sights

Hello allow myself to introduce.....myself my name is tony and i own a small family run pizza shop in queensland australia. in my shop i have a retro arcade game area with at present 12 machines , i have a midway terminator 2 judgement day game, which has had the 2 moving gun sights vanish from the screen, one dissapeared about 2 weeks before the second one did. the game still has the gun sound when the triggers are pulled and all seems normal with everything else would anyone here have any ideas on what the problem would be and how to fix it please regards tony

http://thefratellipizza.wix.com/fratelli