JLC MC Sector Chrono got new shoes courtesy of Bulang & Sons. Vintage Faded Blue leather strap. Much better looking and infinitely more comfy than the OEM Alligator. Looks a lighter blue in real life than in the photos under artificial light.
To make the 20mm strap fit the 21mm lugs I added Viton o-rings, which I cut in half and inserted either side to center the strap and cover the exposed spring bar. Worked better than I imagined.