oh the opposite side of the fire select is a little plastic C shaped peice that is part of the fire select. That c shaped peice of black plastic is loose (when you take the selector assembly out of the slide. The only thing thats holding the peice in when the assembly is out of the slide is a little spring about | | Big. Make sure that both the black plastic piece and the little spring are both there. Im a KSC Distributor and I can get whatever parts you need to fix it, pm me the part number (in your KSC 18c Manual) and Ill have it imported for you in the next order. Good luck
sorry for blurry image, but my phone's camera sucks at closeups and my laptop's camera is getting fixed at the moment
If you are missing that peice or the semi circle peice below it, your selector axle will not be aligned properly, potentially causing your selector to not be in the right position. and the springs keep the tension on it allowing the non circular selector rod to rotate freely (while attached to the semi circle peice)