Auto Transmission Dodgy Replacement

I have a 1994 Nissan Maxima that has done 225,205 km - I recently had an autoshop install a replacement transmission not once but twice.

The first time it was done after 30 minutes driving the transmission would not go into reverse or neutral - I took it back to them and they advised they would sort it out and fit a repalcement transmission if necessary.

I picked the car up today and on the way back home, whilst stationery in a que of traffic at the lights, the auto transmission failed completely - no gears whatsoever.

I pushed the car to the side of the road and found that the transmission fluid all over the road at the point where the car lost all gears.

The garage advised the transmission plate at the bottom of the diff had been peirced by a rod or some other article whilst the car was being driven down the road - this I do not believe as the car was stationery when it lost gears and prior to this was travelling in a cue of traffic at approx 5 km or less for about 5 to 10 minutes. There was nothing on the road that could have caused any holes and the undercover housing was still in place.

They have said they can replace the plate at the bottom of the transmission/diff but can't guarantee it, the workings of the transmiission, will function.

Any ideas or suggestions i? I think it is shoddy installation or/and a poor replacement transmission or both. Possibly the internal selection mechanism or where the transmission connnects to the dif has broken a seal or something was not in the right place when it was put back together.