Klaus,
The strut mounts break in the front suspension on the top. When you remove the plastic strut tower cover underhood you can clearly see the broken mount with the shock rod just rattling around, surrounded by what looks like rubber sawdust. Interestingly the original part and all fresh replacement parts from Volvo have the same date code stamp of May 1998. Obviously Volvo bought a lifetime supply in one shot in anticipation of the S80 volume being a lot higher than the reality of its sales history could justify, and they ain't throwing away those dry-rotted seven year old rubber parts until they sell out. The point being that you can keep replacing strut bushings all day long, and the part you're putting in has the same deficiencies as the part that failed. Unfortunately there are no aftermarket replacements available as best I can determine, and given the modest volumes for this car, it would be difficult for anyone to justify the development costs.