I dont have a 129 but a lot of the issues apply to the 140 body. The pulldown is controlled by a vacum punp which causes the latch to retract untill it catchesa step in the locking mechanisim a few seconds later the vacum is released. Maybe the pull down is not far enugh to let the catch "catch"!. There was a post somewhere that caimed the pull in should be a little father, and then relax. If you manually close the latch the retractor should pull in and you should be able to notice the latching action, and then hear the vacum release. MB checked mine by applying vacum with a hand tool and then observing the bleed down. It turned out to be a bad pump very common on the 140. The later cars had a trunk release if you held the unlock button, but that would completely open the lid. I hope this helps.