240D Automatic Transmission

Today as I was in the driveway I put my car in park and let off the brake, then the car kept going forward! There was a clicking sound as well. After about three minutes of changing gears it finally stayed in park. It seems to be all a matter of an exact positioning of the gear shift. Anyone have any ideas what's wrong with it?

Thanks, TXBill. I hope all I need is new shifter bushings, and that it's nothing more serious- or expensive...