I'll chime in here as I too have broken one of these metal hexes. I do tighten the wheel nuts fairly tight since no one likes to destroy a wheel from a loose or missing nut. I replace the nuts often also... fresh nylon on new nuts is always good! Sounds funny eh? :O
So, I broke one at our Tamiya Championship Series race we had back in February, so I showed it to the TamiyaUSA rep we had running the race weekend and he said he would ship me a new pair when they got back to California. Luckily, I had spares, due to me thinking I would lose them somewhere in the future. Well, instead of losing one, I broke one! Anyway, about 2 weeks later, they arrived! Needless to say, I ordered one or two extra pair as I knew they had a chance of breaking again!
The shim idea sounds good! I'll have to look for some when I get home.
