Is the elastic on the centerbar loosing its stretchiness? Not sure if the AP2s even have that, but I know my '03 did. When the elastic goes (it pulls the centerbar back when putting the top down) it can bind up and cause problems/stress in the top because it's not folding correctly into the bin.
. . . otherwise, there might have been something that fell into the lower top mechanism. This was something that happened with my second car. Found a box of perscription female constipation meds

that was getting all chewed up in there! I always thought constipated women drove BMW 5 series.
Get out of the car with the top down (in different positions if possible) and take a look down into the hinges right next to the seats. You might need a flashlight if the sun isn't high enough.