I was driving the x540 across the yard (not mowing) when I heard a strange sound. The next thing I know there are sparks coming out from under the tractor. I shut it off, looked underneath and found that the electric clutch had come off. And then I found the retaining bolt and saw that it was broken.
I took the tractor to the dealer and he told me that although not common, he has seen this before. He believes that sometimes they come over torqued from the factory. They are a real good dealership and I trust them completely but it just seems odd that it would take 2 1/2 years for an over torqued bolt to break.