I have the same problem with my 2003 156, you need to fit one from a facelift 2004- car in order to make sure it doesn't happen again. A new screen from mangoletsi.com is £394.76 plus vat and the replacement cowl is £79.86 plus vat.
The newer infocentre is slightly different from the old style one and therefore requires the new cowl too but apparently it plugs straight in to the pre-facelift dash.
A direct replacement for the old style one is about £50 from a breaker and a second hand new style one is about £150. I am having mine replaced in a few weeks and will let you know how I get on.