Shocks are best replaced if they fail the bounce test. There are no serviceable components within the cylinder and the cost would just be too high.
Replacement is your only option and always replace as a pair, gives you the chance to alter the vehicles' characteristics too!
In days gone by, you could get cartridges to fit into the cylinder of a McPhearson strut, but I doubt this repair is available now days.
blue skies
tony