Thanks for the Citroen service site! That's a wonderful resource, though I couldn't confirm if the gearboxes are interchangeable. There was no information of the engine clutch housing for my car so I can't compare it with the other car. And the gearbox codes were different, maybe because the ratios of the gears don't match. Maybe it would be ok otherwise, but I can't confirm that.. I'll probably take the 5th gear apart today and see if it's just the needle bearing (234311, that was correct) that needs fixing. It's possible that those metal needles have done some damage inside the box already so it might be just better to change it completely.. Thanks.