http://members.aye.net/~bspen/percterm.html

When you pull that lock make sure the hammer is in the down or half cock position. You hit that arm of the sear and release that hammer and it hits your thumb you are going to know it. Also pay close attention to the sear, fly, and tumbler. That is where they normally gunk up.

I take the whole lock to the sink. Fill it with hot water and some dish soap and using a bottle brush, scrub the devil out of the back side of it. After that I spray it off with brake cleaner or carb cleaner and then wipe it down with paper towel until it is dry. Then I use aaerosol oil called Birchwood Casey Sheath aka Barricade and mist the back side of that lock. Then using Q-tips I like to wipe off any excess oil. You will be surprised how well this makes the lock function and speeds it up.

That link about might help you with what to look for.... Good luck.