transmission not registering "park" position- shift to park

Sometimes when I put the car into park, I get repeated warnings to "shift to park". If I don't jiggle the button on the shift knob, my seat and other electrical components will not respond. I press the shift release button several times then the warning stops and my driver seat functions to allow me to get out of the car. This is a pain and the dealer said that if the problem couldn't be duplicated while in service I would still get charged over $200 just for diagnosing and technicians time. (Even if the don't see the problem) so thus far, I have chosen to not take it in for service and risking paying $200 for them to tell me they can't find the problem.