It's rare that I see the parking pawls broken on these things but when they do come in with a broken one, it's almost always due to the driver allowing the full weight of the vehicle to slam the pawl after putting it in park on a slope and not setting the e-brake and/or pumping the brakes a bit to allow the vehicle's weight to come to a gradual rest onto the pawl.
Guide plate can also be installed wrong preventing full contact...
When going back with the unit on the bench, always test the parking mechanism to ensure the rod will engage the pawl and the pawl engage the lugs on the parking gear (which is part of the rear ring gear in 700R4s/4L60Es) and arrests any movement of the output shaft...Sometimes you'll have to turn it a very small amount until the pawl is able to slide into the next gap between the lugs...
Guide plate can also be installed wrong preventing full contact...
When going back with the unit on the bench, always test the parking mechanism to ensure the rod will engage the pawl and the pawl engage the lugs on the parking gear (which is part of the rear ring gear in 700R4s/4L60Es) and arrests any movement of the output shaft...Sometimes you'll have to turn it a very small amount until the pawl is able to slide into the next gap between the lugs...