82 380sl trans not engaging in any gear position

[dad380sl]

It has been several months since I completed the swapping of a 5.0 liter 117.961 Euro engine into my fathers 1982 380sl.
I drove the car about 4days ago and yesterday, I decided to take her for a drive but it would not engage in any gear. Nothing at all. No reverse or forward in any gear position the car just would not move. This seemed odd because I had just driven the car a few days ago. I was only able to check fuses and all linkage bushings were also replaced when I was doing the conversion. I'm just baffled at what this could be. during my search for a cause, many pointed to a failed pump, but i can't justify that the trans pump just decides to suddenly quit. Therefore I am thinking it could be something else.