If the struts (front has struts) show no sign of oil leakage and operate quietly they are just fine.
Failed struts will display external oil leakage (seal failure) or a rattling noise (deflected disc breakage) over bumps.....almost a 'jingle' type sound.
Many struts get replaced because they fail a 'bounce test'.......all fully broken in struts will fail a bounce test but the installer or provider of struts will not share that information.
The majority of struts are replaced needlessly as a result of this method.......and because few people understand how a strut works.
Quite simply, a strut, due to the damping oil control orifices (deflected disc pak) only dampens at the rate it was compressed.
By pushing up and down on the fender you are only mimicking the gentle rise and fall of the road....very little damping is required.
If a strut is stroked rapidly, like going over a rough railroad crossing, the deflected disc pak will restrict damping fluid at the rate the damper was compressed.
Bottom line......struts are actually considered a life of car component......but if I made a living selling suspension components I wouldn't share that information.
Now, the shocks found on the rear suspension of the Cruze are fairly traditional, gas charged units......the gas is nitrogen btw.
These, like any shock (damper) use a piston with rings that ride inside a finished bore in the shock housing.
The piston has orifices (little holes) that the damping fluid passes through as the assembly is stroked, damping the motion.
Over the miles, the rings wear out, and the damping fluid passes the sides of the piston as well as the controlled flow through the orifices.
Suspension control suffers.....and as the miles accrue the shock is, for the most part, just going for the ride.
Operators don't notice the degradation because it takes thousands of miles......when replaced, most are surprised how poorly the car was handling.
All this to tell the OP that if the strut bodies are dry, leave them alone and, due to mileage, it is indeed time for rear shock replacement (inexpensive maintenance).
I will embellish the strut thing though.....just a bit....and I said this in a post about a year ago as well......a new strut will indeed pass a bounce test.
This is because the strut seal is new and very tight around the strut shaft. (Called Sticktion....aka Seal Friction)
This extreme tightness is perceived as a improvement when, in fact, at about the 5000 mile point when the seal is fully broken in, the new strut will respond to the bounce test the same as the, still serviceable, strut that was needlessly replaced.
Rob