Hey, Waterloo -- There is a long discussion about this topic
here.
You can ignore the long discussion and photos of capacitor replacement -- somewhere around page 5 or so of the thread is a link to a great little utility by Mike Spikel that solves the problem. The long and short is that your capacitor is likely dead, and that his utility saves the clock info while you change batteries. I have also found that I can save the date and time if I change batteries with the unit plugged into AC power.