Often the problem is loose or missing screws in the mountings, but the detent near the scissors pivot point can be tricky to function properly also. Ours was missing a mounting screw (or two) right from the factory, but even with that rectified, BCS eventually replaced the arm after I only had some minor success trying to get it reset. They originally tried just resetting/replacing a couple of fiber shims in the door frame, but as best as I recall that was mostly to cut down rattling, and the shims never stayed put. A properly mounted arm shouldn't rattle on the road anyway. One fiber shim remains glued to the top arm at the center pivot, where it intervenes quite capably between the assembly and the top door frame.
David's issue may be from one or both of his mounts; I wouldn't think just the center pivot being worn would allow that much sag, although it certainly would compromise the detent and catch's function in holding the door open. If the whole thing is worn to a point of sloppiness at the center pivot, or the mounts aren't aligned right or are loose, then the detent and small "catch" there won't hold. Ours has worked very well ever since replacement (9+ years?), staying open even in winds and yet being reasonably easy to disengage for closing.
I've run across many owners who never realized their doors were supposed to stay open if needed. Either their mounts were loose or the pivots worn to the point that the detent and little extruded catch couldn't do their job. You should be able to check for excessive sloppiness of the arm by just holding the door halfway open and standing on a step or a closed step cover. Then fully open the door and examine the detent and catch assembly's performance in place. If it's all too sloppy and it isn't one or both poorly set or aligned mounts, then I'd replace it with a new arm assembly - the detent, mini-extruded catch, and center pivot have to perfectly work together, and may not be worth the time to try rebuilding.
That said, one could try removing the mechanism's door and frame mounts, taking the assembly to one's shop vice if available, and squeezing or ball-peen hammering the three pivot "rivets" to see if they could be tightened up at all. I never got to that point with ours, and having not actually had the mounts off I don't know how feasible that is But if anyone is up for giving that a go, let us know how it works out. I suspect David has access to the resources for that.
Joel
