When idling, clutch in, is it hard to get the car into gear? Or does it feel like it has a few notches before fulling engaging? I have no idea about the vibration, but I imagine it is simply a piece of rubber that was on its last leg and decided to go. Where does your clutch engage as far as the clutch travel is concerned, bottom of the stroke, top? If the shifter bushing were to be completely removed wouldn't the shifter just shake around with the vibration from the motor? I recently drove an old 318i and its shifter bushing was completely shot and I could feel vibration in the shaft when holding it. Who knows, haha? Goodluck though.