My 04 reg has developed a problem with the tailgate, it's been popping open now & again while driving, today it wouldn't stay shut when i slammed it, gave the latch a squirt of WD40 & it shuts ok, problem is it won't open again, well it does perhaps 7/10 times when you try it, tried locking & unlocking the car makes no difference, when it won't undo if you leave it 30 - 60 seconds it will open most times