How to tell if your struts/shocks need replacing?

1. How many miles on the odometer? If more than 60K miles are logged by the struts/shocks and if you are concerned about the ride or hear suspension noise then it is reasonable to suspect those parts.
2. If you see oil leaks deposited on the body of the strut or shock then the part definitely has failed. However the lack of oil does not prove the part is good.
3. Certainly if the body is not well-controlled under normal and simple maneuvers like parking, I would replace the struts/shocks now.
4. I have posted on how to DIY replace both the front struts and rear shocks.
Hints Regarding Replacement of 2G Front Struts | PriusChat
Replaced Rear Shocks | PriusChat

 

All strut manufactures stress 5 year/50,000 mile replacement interval to maintain OPTIMUM ride/handling quality. After swapping out my fronts and rears, I'm a believer in the strut manufactures claim. Before I had thought this was their attempt to get people to change the parts out unnecessarily; kinda like some shops still saying 3months/3,000 mile oil change intervals (absurd given vast improvement in oil quality and engines). To convince yourself:
Read post #48 for fronts. Hints Regarding Replacement of 2G Front Struts | Page 3 | PriusChat
Read post #3 for rears. Replaced Rear Shocks | PriusChat

If you want a softer ride, go Monroe. My buddy who went w/ Monroe and it definetly feels softer than the KYB's I went with.

 

I wouldn't put Monroe shocks/struts on a vehicle I intended to keep. In my experience with them on other cars, their quality/durability/longevity is severely lacking. A quality part (KYB, Bilstein, etc.) will last at least twice as long, and give superior performance while doing it.