Leaking hatchback boot - how to move lock mechanism downwards

I have leaking boot problem, during rain I've observed via the rear seats and without opening the boot water dripping from around the almost horizontal section of the hatch approx halfway along one side, and to a much lesser extent on the other side. The seal seems in good condition and so I don't see how replacing it would improve things.

I then found this on octinfo.com http://www.octinfo.com/index.php?p=used_tip_o2_en

"Wrongly set trunk locking mechanism. Some cars made in 2005 have wrongly set trunk lid lock mechanism. The whole mechanism must be moved downwards by 1-2 millimeters."

I had thought that the boot didn't make a particularly solid 'thunk' when it is shut, more and empty hollow click (although the body panel alignment seems fine). Nonetheless I'm suspect this could be my issue.

Has anyone done this? Is it easy to do? Is the lock designed to be adjusted or is this more involved that just a screwdriver job? I haven't had a chance to attempt it yet.

Cheers!