New fuel pump installed...and as expected, the fuel supply hose fitting had failed. You can see in the photo that the plastic clip that's supposed to grip the pipe on the bottom of the fuel sending unit has failed. The "buttons" on either side should be popped out, proud of the fitting...but they're not. The plastic had, over the years, simply lost its ability to spring back to shape once the buttons were released. Thus, when the fitting was pushed onto the pipe and over the flange, a weak "click" was heard...but the clip's grip was so weak that fuel pressure would force it off the pipe.
In summary, if you're like me and have a failed fuel sending unit on a 986, you may want to consider replacing the fuel pump while you're at it. In my case the pump still functioned properly, but the fitting had failed and left me on the side of the road. At least now not only do I have a functioning fuel gauge, but a new fuel pump as well. One less thing to worry about.