My upper strut mounts have been failing after a year (about 12,000 miles, typical highway and local street driving, no off-road!). This seems to have started when I replaced shocks with Bilstein slightly stiffer variety. I also put a stabilizer bar on it at that time.
Do you think the shocks are the fault? What else might I look for?
If the car has high miles on it then the proper practice is to replace the mounts when the struts are changed. If this was not done then odds are they’ve just met their projected lifespan.
There’s also the possibility that whoever did the struts did not perform the job correctly by leaving something out, failed to tighten a strut shaft nut, stock mount did not fit the Bilsteins properly, etc.