Oops... I guess I haven't been watching the thread.
Werner: I think main problem was that previous owner just didn't bother to tighten it when it first came loose and it just kept getting worse. It finally got to a point that it really needed to be replaced completely to get 'er done right. The barbeques won't start back up until next Oct/Nov, when the Canadians start coming back down to go to the Bahamas. The marina is pretty dead right now (except for me).
Carl: If I understand what you mean, you intend to make the holes slotted across the width of the plates. Not only is there is a lot of weight on those brackets, but a good deal of pressure while opening and closing. I would be concerned that you might just make it even more likely to loosen up again... especially using just screws. I think if you put them exactly where they need to be, you'll be better off. Just my 2 cents.
Rich: I found the same method to work with the short slides. But mine had been left loose for so long that the screw holes had become craters and the slides just fell off. When I removed the hatch (and seahood) to replace them, I decided that the longer slides would hold the top better and prevent water ingress if hit from the side.
Thanks for the feedback.