How to repair a Baldwin door lock?

I have a problem with the Baldwin lock on my front door. I do not know the model number. It was installed in the past 20 years. I looked at some sites to identify it, but do not find an exact match. It is similar to the Atlanta model shown here: http://www.designerhardware.com/Baldwin_Atlanta_Handleset_p/bld-6570.htm
The lock is a mortise lock. On the outside there is a hand grip and thumb piece above it and a key cylinder above the thumb piece. On the inside there is a round knob and a key cylinder above it. Looking at the door edge, there is a deadbolt near the top, a latch mechanism (don't know the real name of this part) below, and two buttons below the latch mechanism. If the bottom button is pushed, the thumb piece on the outside of the door can be pressed down to open the door if the deadbolt is not engaged.
The problem is that when the thumb piece on the outside is pressed down, it draws in the latch mechanism, but leaves about inch of the latch protruding outside the door. The inside knob can be twisted to withdraw the latch almost all the way into the door. The latch is free to move because it can be pressed in easily with your finger.
Before I tear into the lock, can anyone offer guidance as to what is wrong and how best to proceed ?
PaulF
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Paul Ferguson wrote:

As you start taking things apart, You are likely to see that it is a rather simple construction. You may see the fix or at least see what parts are involved. Take those parts to a good locksmith and see if they can provide replacement. If not you may need to replace the lock.
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Joseph Meehan

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On Mon, 05 Sep 2005 16:37:10 GMT, "Joseph Meehan"

Thanks. I looked at how to take in apart and was not completely sure what to remove. I squirted some graphite powder in the thumb piece opening and it seems to be fixed. I should have tried this first, but it did not seem like the usually sticking problem.
PauF
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Paul Ferguson wrote:

Glad you got it working.
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Joseph Meehan

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