slider locking mechanism

I have two of these doors, from the 80s I think.  The first two photos are of the door I did not take apart.  The mechanism in the other door was not working correctly, so I took out the screws thinking I could remove the mechanism.  But when I removed the screws, the mechanism fell down inside the door to the bottom.  The other three photos are of the inside of the inner handle.  The lever is still there.  Is this mechanism replaceable?  If so, please give instructions for reassembly.  Thank you.