Intermittant speedo

[BBBurban at aol.com]

Hello all.  I am looking at several urS4's for sale and one that I test drove 
has an intermittent speedometer.  When I pointed this out the owner's 
response was that he doesn't want to "quibble over little things."  The 
speedo seems to go in and out both on it's own or if striking the instrument 
cluster.  Does anyone know what might be wrong with this and what the 
possible repair cost would be?  

Thanks all

Hank