It's interesting to note that unwinding a gearbox was the nail in the coffin for many 2cvs in the uk, in the early 90s we were always being sold cars which were otherwise good but with 'broken gearboxes' that turned out to be simply unwound.

I'm suprised that Vikings not seen it more often in his 20? Plus years as a Citroën man, maybe it's just us Brits who need to franticly reverse everywhere? I've done two now, and can think of endless others that have occured.

I learnt my lesson the first time (200 miles jammed in 4th) and it turned out the second time the box had already been done not long before I bought the car, but not very well, I was reversing downhill at very slow speed!

Unwound gear box is not the same as the 2 rear nuts being loose.
I have seen plenty of loose nuts in my time (some using this forum, ) but only seen one spinding off. The shaft is forced backwards and punch a hole in the rear cover.

Mine did, the peening didn't hold as it should. From 1985-86 the sliding pinion is made with softer metal so the peening can open. I no longer use a center punch but an old flat screw driver. Before 1985/86 the metal was made from harder material so fewer problems there.