hi guys,
i had the same issues on my 20carbon as Mike. Problem was that the cleat is designed for robe-diameters from 6mm onwards. Nacra is using 5mm spin halyards on their race package. just splice a 3mm dyneema inside the area you want to cleat AND Mount a screw with sleave (10mm) through the holes under the cleat. this will protect the stainless base from widening while load is on the cleat. since then no Problems occured.
greetings from Germany
Ludger