Happened with my BX. Couldn't say what the box type was.
Ascending a long ramp there was a loud bang but nothing else.
Parked, went into Asda, came out and saw fluid under the car and presumed an LHM leak.
Checked the LHM and it was OK. Started the car and it rose as it should, drove home, called a local Citroen specialist and he had me take it down the next morning, about an eight mile drive.
The sun gear had broken and smashed a hole in the side of the box, the fluid was the gearbox oil.
I was amazed that there was nothing to indicate a gearbox problem.
He stuck a replacement second-hand gearbox in that he had in his garage and all was fine.
Until the head gasket went while my daughter had the car at the other side of the country
