Strut replacement
"My Dad's a TV Repairman"
Joined: Jul 2014
Posts: 471
Likes: 153
From: San Diego
Welcome to the forum. There is no recommend mileage; it all depends on how the car was driven previously, whether they're leaking or not, how much rebound they still have, and what type of suspension you have (Z51 rears will typically last quite a bit longer than base).
How many miles do you have?
I would not simply replace the rears; they should be replaced as a set, and can be done with very basic tools in about 2 hours total. Look into C6 Z06 shocks- they're great, and can be bought brand new for less than $300 at many outlets.
As far as testing them, open your hatch and place both your hands on the seal area (don't push down on the painted rear fascia)- Then push down rhythmically, and see if the car goes down too easily, and worse, self-oscillates up and down after you stop.
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Joined: Mar 2001
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From: In a parallel universe. Currently own 2014 Stingray Coupe.
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If you are talking about the shocks on the car (wheel area), then Fed Up has you covered. For the hood support or trunk support, then not2old gave a good response. 
Le Mans Master
Joined: Feb 2012
Posts: 6,644
Likes: 479
From: OK
The C5 has shocks... C6 Z06 shocks are a nice upgrade
They are a direct fit... plug and play...They can be found on the C6 for parts for sale section sometimes or Cultrag a forum vendor offers them as well....
