Navigator intermediate steering shaft noise??

[tosaman]

I have a 2005 Navigator that has developed a "klunking" sound when I go over bumps. My first thoughts were worn bushings or a loose tailpipe hanger, however, my local Ford dealer said the only thing they could find was that the intermediate steering shaft was loose and wanted over $500 to fix it (I assume replace). Does this sound right, and if so, is this a replace job or simply new lubrication? Thanks.