If it is used then the first thing I would do is get a total oring rebuild kit. Replace EVERY oring in the thing and clean it up as you go. Go ahead and keep all the old orings if they look like they are in good shape for later field repairs.
I always add $10 in my head when I purchase a used marker for a total oring rebuild if needed and as of right now I own 60+ markers and 50+ of them I purchased used.
-Tim