I am trying to remove my rear brake rotor on my '87 190D and am having difficulty doing so. According to the manual that I have, once the caliper has been taken off there is only one 'lock screw' to be removed. This had an allen key head on it and I have removed that and the disk still seems like it is pretty well attached. I've tried banging on it and pulling on it pretty hard. Is it just stuck or is there something else that I'm missing?? Thanks for the help.