Originally Posted by Rolf
I get what you are saying and yes it should technically not move. You are however supposed to keep it from rolling with the hand/parking brake with the trans in Neutral before shifting it into Park.
Most auto manufacturers will say the opposite about any vehicle with 4 wheel disc brakes, and that putting it in gear (manual) or park (auto) is the "proper" way to keep it from moving. Modern parking brakes are very small drums that won't really hold up to much.
Vehicles with rear drums have a much better parking brake, but if it rolls freely in park, there's definitely an issue
I'd disconnect the linkage from the trans, shove it as far into park as it will go at the transmission, and see if it rolls. That would be the only practical way to determine if its an internal issue. You can't check the pawl without dismantling the trans, but the odds of it being internal are lot lower than it being linkage. The difference between "almost in park" and "in park" at the linkage is close enough that it wouldn't be obvious by looking at it. (Its a few mm difference)