Shower leak update: plumber did a leak test. Shower pan is officially leaking, probably from where the shower pan meets the drain. Also there's evidence that the tiles were installed wrong and never sealed. In short, it's going to be an insurance claim, blowing wildly through our deductible.
The next question, of course, is if we want to soup up the bathroom while we're at it. His and hers showerheads? Constant/regulated temperature valves? I'm personally tempted to tear out the jacuzzi bathtub, which we never use, and go with a bigger walk-in shower.