There was much kerfuffle, but minimal actual damage, since the basement is unfinished and there was less than a quarter-inch of water at the most. We managed to get the part replaced yesterday afternoon, and are now drying stuff out. It came to a few hundred bucks for a shop-vac and plumbing costs, some hours of hassle, and an opportunity to get rid of stuff that we don't really need and never use anyway.
The plumber's diagnosis of the cause of cracking was overtightening in the original installation. If you do your own plumbing work, it might be wise to keep in mind that too tight is as bad as too loose.