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Replace the swivel clip of your harness without any sewing as you keep the original part sewed into the webbing.
Note The cheaper Natural Versatile Plastic's locking finger only flexes a few time before snaping off. Once fitted you should not need to take it off again, the more expensive Premium Versatilre Plastic should last much longer if you think you wll need to unclip the hook more often.
Break out old lock ring and pull out broken clip, Fit new lock ring (note there are variations in the thicness of this ring across the production of these strollers you may have to sand the ring down a bit) the and push new clip up into the new lock ring.
Check you clip against the 3D image to make sure you have the right clip Bugaboo changed the style/ size of the "lift guard" inside the clip. I have three versions of the Bugaboo Shoulder Clips on Shapeways so the one you need will be here. It is most important that you do not try and force fit the disk into the slot. You may break that part of the harness clip. I can send a replacement end but it does require unpicking of the webbing and resewing back in. The locking disk is easy to sand down to a smaller size if needed. I will update the clip files and reduce the disk lock by 0.2 mm. You will know I have done this when they revert to "First to try"