ok, those black corner caps did come off and whew we had the right tool to get those bolts off (they're not regular screw heads, they're the star ones). i'll indeed be glueing and clamping that flappy plastic part to the metal frame behind it, you're right it looks like they just had some double-sided tape and it's gotten hard and is peeling off...
one more question, the two corner caps that i popped off with a screwdriver, each has 2 plastic posts with little silver teethy holders... three holders came with the corner caps, one stayed on the main part of the roof rack. does this matter when reassembling?
thanks for all your suggestions and help!
-heidi