ignition contact problems.........

the piece of plastic that is screwed to the back of the lock cylinder, seems to not always make contact.i checked the screws and they were loose so i tightened them.it is again acting up though. could someone please tell me the part i need to buy or what is wrong.it is all most impossible to reach the upper screw and it seems the only way to remove the cylinder is to break or file off the tamper proof factory rivets.could someone help me out?

thanx shawn