In response, and I pretty well know now...
1/ You dont need to remove the floor panel. We removed the screws inside the drop-down side panel(Where the antenna/rear washer bottle and first aid kit lives), then the two screws holding the rear seat belt guide. Remove the clip.
Then we pealed back the door weather strip, and levered the clips off, so allowing space to see under the trip piece and see the mechanism.

2/ We wanted it fixed. I just used what I had to make it work... I think it will not come off that lower latch again... but I bet the upper will break first!

I will admit, I could not have done it without my younger son... its not his car, but he was keen to help and loves a challenge!

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2009 Mercedes ML320 Bluetec