Car is back up and running. Here is a few pictures with description. I'm not sure what could have caused that, except, well after a bit of thinking it must have been a gremlin.
The long finger on the left goes in the hollow part pointed by the screwdriver.
On the left is the rod that moves to put to reverse. It is now in front position when i opened the case it was not protuding.
Here we see the what move to change the gears. The small finger on the first piocture goes in the slot.