Please help identify a convertible top part

[Juggernaught5]

Hi all:
A plastic retainer has broken off my top on the driver's side, causing the interior liner to sag, and the plastic header to rattle annoyingly. From the break on the part, it looks like it's part or a larger piece/frame. I can't identify a matching part on BMWpartssource.com or realoem.com - there's not enough detail to the drawings.

I'm a bit wary of taking the top apart to troubleshoot - thought I'd see if someone who has worked on their top can help.

Thanks in advance!