Yeh, I got one fitted to my 156 under warranty. The seals on either side of it were shot and the front suspension was rattling like the shocks were knackered. It turned out to be the anti-roll bar.
Took a couple of weeks for the dealer to get his hands on one. Then the best part of a day to fit it. But after that the problem went away.
I've a 01 Sportivo with stiffer set up. Road surfaces here are crap so it takes a bit of a hammering. The anti roll bar is exactly the same one as used in the Fiat Marea and it has a weakness they've known about for some time.
Yes the handling went off and the car felt wobbly at times coming out of a corner. This cured it.
Sorry Harp, I was away for a couple of days. The mechanic in the dealership that sorted it told me about the Marea/156 anti-roll bar problem. The seals at either side go after a bit of heavy usage apparantly. It's not dangerous though - at least I don't think so. Just rattles about a bit.