Just purchased a used Seville with 60K miles on it. The right rear shock is leaking fluid. The car seems to be running fine, don't notice any problem yet in the ride. I was told to replace both rear shocks (at a cost of $700 each from the factory)! I found them for sale on the internet for $300 each (OEM - 1 yr. warranty). The equivalent Monroe shocks are $400 each (lifetime warranty). Any suggestions?