sliding door to deck - latch mechanism no longer working

Thanks for reaching out! The handle you have can be replaced with either the 82-087 Legacy Keyed Handle Set or the 82-090 Legacy Handle Set. The only difference between the two is that the 82-089 is not keyed.

Your mortise lock reminds me of the 82-229 Mortise Lock with Pocket Trimplate, which is compatible with either the 89-020 or the 89-021D Diecast Keeper.

Alternate view of 82-229

Alternate image for 82-229

Alternate image for 89-021D

Is the mounting plate, in between the handle and the mortise, a part of the mortise lock hardware? Or is that from a different lock. If that is part of the entire locking mechanism, you'll need to include that in your measurement to confirm accurate dimensions.

Please feel free to reach out with any other questions

Thanks for confirming this information. I would suggest double checking the diagram from the 82-229 I recommended to you. This mortise lock, is the one you have but your pocket trimplate has been removed from the assembly.

The compatible keeper would be the 89-021D, this is the piece to the far left.