The broken part looks like a magnetic reed switch.  Looks like there's a float with a magnet in it that activates one or more switches as it follows the water level up and down.

Radio shack used to sell them (maybe they still do) and they're commonly used in alarm systems to detect a door or window opening (although those will be encased in plastic)

They are available in normally open and normally closed types. Since the failure causes it to read as full, I'd guess the switch is normally closed (opens when near a magnet)

Of course, I'm guessing this based on a photo, so I could easily be wrong.

>>> Go to this site: http://picasaweb.google.com/ewieber
>>> Thanks, Ed
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