Sorry, I thought I explained it better than I actually did. This issue is only apparent when the slide is extended/open. All works and seems fine otherwise, it's just something that I had noticed. From about 18 inches down from the leading top corner, and then across the top of the slide for about 2 foot or so, there is a gap that increases as you move toward the corner to a point where at the corner, there is about a 2 inch gap. The shop foreman and his tech thought there was a 'warp' in the floor so that when the slide gets to full extension, that top corner just doesn't seat off.
The Dewald slide locks all work fine also, but are not involved in this situation. I was hoping somebody that had seen/corrected the same issue might chime in since the foreman said he'd seen it before. Might be a Monaco build issue.
As an addition to this, and possibly a clue. The previous owner (not the original owner) only had it a couple of years. I found when cleaning/inspecting the coach for the first time, two home made looking tubular shaped things roughly 30 inches long, that I have since determined were made to fill this very gap. This must have been an issue from some time ago.