Sliding Glass Door Mortise Lock Replacement
In order to replace this lock, I needed to take the door off the track and then dismantle the aluminum frame with a block of 2x4. Once apart, I unscrewed the locking mechanics and then rotated the lock 90 degrees inside the aluminum channel and slid it to the top. (It would not come out of the bottom.) To replace the lock, I followed the same process in reverse.
It's a shame that the whole door had to come apart to replace a $12-13 part. But I am glad it is done. If pictures are needed for someone else, I will be more than happy to post some.