are you talking about the little oscillator/match piece? little plastic piece that has a little claw thats spring loaded. Its is dragged across a "cog" to determine which number is the match number? also controls the oscillator so if you dont have lights going left and right during play that would also point a finger at this little troublesome piece of )^&*^^^)!
it his is what I think it is, usually mounted up there in the head, this little unit is broken a lot. a real lot. THat part is actually available to purchase. Had a hell of a time finding one so I bought 3! Of course I cannot remember where I bought it.