Have you had any other issues in the past with your shoe itself? Why I ask is we had our chaffer work loose on one of our L2's and it cracked the shoe up pretty bad before we noticed it. We pulled the shoe out and fixed it and beefed it up some. Put the shoe back in and immediately it started taking the rubber bushings out daily. Spoke to the shop foreman at the local dealer and he said those shoes are perfectly balanced out of the factory and extremely important to keep them that way. We had to pull the shoe again and balance it up sum. Still not perfect but it does better.
A couple other things you might want to check. How much gap is in your sway blocks along the side of shoe? With you combine sitting on perfectly flat area I think it calls for like a 1/16th of an inch gap on each side. Check your book for sure I can't remember. Also how are your bearings on the crank that connects to the shoe? We've seen those get a little play and cause troubles. Also make sure those cast iron connecting arms are perfectly straight and aligned. If their froze up some on the bearing they can get a little cockeyed and take those bushings out quick. Good luck I hope you find the issue. Trust me we know how frustrating it can be.