Lots of times flushing won't do, especially with an older pistol.
The firing pin is pretty easy to take out. This link will help. The only place your pistol may vary is the right side on the safety. Some have a screw, some have a small pin that must be depressed while you slide the leaver forward to remove it.
http://www.*************************...sassembly.html
Edit, this site won't let me post the link. Go to the other S&W site in Gunsmithing to find the info. Here's a youtube vid of the process.
http://www.youtube.com/watch?v=Vx7g2...eature=channel
I'd also replace the firing pin and recoil springs just because you don't know the round count.
Dave