I bought a used 14" 870P police issued shotgun and am waiting for my stamp. I got a really good deal on it as with the shotty & stamp I'm still less than what a new 870P costs. Externally it is in good condition with only minor scrapes. Doing a function check I noticed the slide wasn't as smooth as my brand new 18" 870P. What are some things I should look at and what are some things you would do to refurbish it? Any recommendations welcomed, Thanks!!!!!!