Tribeca thumb latch replacement parts

A home owner from Central Florida says:
What other internal part should I replace besides the Tribeca failed thumb latch which has become very loose? What is meant by an internal mortise you identify as a likely cause ?
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Bob from SWISCO responded:

Thanks for writing in. The mortise lock is the latch within the door that the 82-043 Tribeca Lock lets you flip to lock the door. If you're uncertain whether you need to replace this or not, I'd remove the Tribeca Lock from the door and then try 'manually' flipping the mortise lock with a flathead screwdriver. If it works, then you know you only need to replace the thumb latch. If it can't flip, then you might need to replace the mortise lock as well. See either our 82-037 or 82-242 . Compare both with your old mortise and see if one of these is what you're looking for. 

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