[PaulE]

There is a sort of screw spiral groove in the spinlock as I recall. The perpendicular pin through the attachment point of the hardtop rotates through it to pull the hardtop down as the lever is turned.
Backing off the tightening of the retaining screw may have allowed the upper part of the spinlock to expand but not the spiral groove or maybe all the way down into the spinlock. Maybe you can remove the spinlock and see if it can go onto the hardtop attachment point with the lever turning freely all the way? It's probably more work than you want to do, but that's all I've got. If you don't want to do that, maybe put a thin punch down into the spinlock and see if you can lever it to open up the spinlock a bit more, and/or some grease on the attachment point before putting it into the spinlock and see if that helps. I've been in the same boat having to do things a few times to get them right on some of my projects!