I have a pre-disk Rohloff Birdy that is getting on a bit but still rides well. Recently however I have noticed that when I pick it up the rear swing-arm hinges downwards rather like a Brompton - in other words the plastic catch holding the rear frame in place is no longer working. Nothing seems out of place, and the catch does not seem particularly worn. I notice that the screw that it clips over is done-headed and I cannot be sure that the previous owner did not replace the original screw for some reason.

Has anyone else had this problem? It’s not clear how you would fit a new catch to the swing arm.