I don't think that the lips themselves have thinned down, just that using a lot of leech tension with the mainsheet, eventually works them open. I had the same problem on Mondial. Apparently this is a known problem with the Kenyon spar, because I was able to get some stainless steel reinforcing plates and then rivet them in place. Even with that however, I use a heavy-duty velcro strap around the boom to help hold the clew down. I have been thinking of grinding down the lips for about a foot and mounting a car system. The one difficulty I see is that the bottom of the slot is not flat, so a filler piece would have to be fabricated.
