Shocks normally get replaced in pairs if used much. If new, then if just one leaked I'd either replace the one with exact same, or more likely, replace both on that axle. If high miles, then the whole set. New shocks come prefilled and are sealed.
You don't want a new one on one side and a well worn used one on the other side any more than you want a leaking one on a side with a just serviceable one on the other side.
Problems huh? Then Read THE Book.
A natural borne "neanderthal"
.________________________________________ ____________________Toreador Red 2001 Mercury Grand Marquis
.... with some minor mods.
I've been hated before.
I still am by some maybe?
... I got over it.