Nasty O/S Suspension Leg Leak. Common??

Had a liitle look under my car today to find that there is a disgustingly bad suspension leg leak on the o/s. Would it need replacing or is there a way to fix this? If it does need replacing are they cheap? and would your recommend buying new or 2nd hand??

Thanks, Reece.
 
if its from the damper unit - it needs replacing and in pairs to do it right