Tim
I just got done rebuilding both of my panniers as they were getting sticky and didn't like to latch/un-latch anymore. Actually, I only was going to only do one side, but the after getting completely lost trying to put the first one back together and had to tear into the second one to see how to put the first one back together! About a 1/2 hr later I had both of them apart and still couldn't figure it out.....just twice the fun now!
I eventually got them back together, but it took hrs of study and fiddling to wrap my head around all the moving parts. For what it does, it's a pretty complex mechanism. One of the posts above said to go slow....do it! Take the inside liner out, but before you go any further, two things. 1- take the time to work the mech until you completely understand how it all works. Fight the urge to just tear it apart or you're not going to like the outcome. 2- Pictures....lots of angles of all moving parts....pictures.....pictures....getting the picture??
What I found with mine was that the grease they use attracts fine dust that works it's way into the inside and eventually it gets gummed up. Brake cleaner and then re-greased it all. If you decide to jump into this, take your time...if you get stuck, I can probably give some help from here if you have pictures.
FYI- there is a small stainless steel gear that is operated by that lever you show in your picture.....it almost hidden and is hard to get a picture of before you take it apart. The thing is, it can go back in in 4 different positions....this is the gear that really kicked my butt. It's slightly triangular in shape with teeth on one of the three sides....NOTE how that part comes out! Also, try to note where the teeth go....as in, what tooth goes to what tooth....trust me on this one.
Also, there's small "C" clips the hold the pins for the handle....they get lost....easily. Dropped one on the floor and it took me 45mins to find. Good luck mate.