The only thing I can think of is a plastic rod that is located in the shifter's shaft (the part the handle is on) or the slider.
The only thing is that if removed the shifter won't work at all. If they removed it and trimed a piece off (a small one) it is very possible that it won't go into park. The reason for that would be that to get in the park position, the detent on the shifter must be fully depressed to get the park position. See these pics. The first is where the plastic part is located.
The second is what it looks like removed (lifts right out).
Another possibility is the slider may have broken into two pieces. (see the last two shots) It must be one of these two that they are talking about, ask them which one.
Was the car parked on a slope at their shop?
Another thought, is your 'T' handle firmly seated and not raised up a bit? If it is the keeper must not be seated properly or the keeper is missing and is at that shop.
The last shot shows the park detent.
[This message has been edited by Indiana_resto_guy (edited 09-08-2003).]