I disassembled the base unit and found two electrolytic capacitors that had failed (leaking on both ends). I suspect this is the cause. Both caps are 6.3v 1000uF (-40-85 C, radial lead). I am going to replace them and see if it resolves the problem. Part number 272-1032 at Radio Shack ($1.59)
http://www.radioshack.com/product/index.jsp?productId=2102511
John
March 2006