The big problem with 159s and Breras lies in the front and rear subframes which are made of iron and are VERY rust prone, depending on climate. If the car was well cared for, they would of been wax oiled and/or removed and painted.
I'd suggest you follow Autolusso's facebook page, as they regularly post photos of cars they are working on. There are lots of examples, both of your 156 problem and of the newer models and what they do to repair them. That will give you a general idea of what to look for.