I appreciate that my answer is unlikely to help the original poster, but may help others. The tools I used, when I had this problem with my 2004 Liana, were a large crosshead screwdriver, a small flathead screwdriver, and a can of spray lubricant. First I dropped the rear seats and removed everything from the boot to give me room to work and a flat work surface, and entered the car by one of the rear doors. I then removed the tailgate trim panel by removing the four large crosshead screws and two plastic rivets which held it in place. The rivets are to the side of the tailgate struts and can be removed, without breakage by pressing the centre of the rivet in (gently) and then removing the whole rivet with a small flat screwdiver. You can now remove the trim with care, as it is attach by several push pins which help to relocate it when you put it back. Having removed it you can see the locking mechanism. To the right, is the back of the mechanism where the key is inserted when unlocking from the outside. Lubricate this mechanism, get out of the car, and try unlocking with your key. If that works, your problem is solved. If not, check the linkage that runs from this mechanism to the centre of the tailgate, and then down to the lock itself. Look for signs of wear or anything loose. Anything worn will need to be replaced, but hopefully lubrication will solve many problems.
Bob, August 2013
