I took a closer look. Its next to the antenna. There is a long rod going out the back of it to the end of the trunk along the fender. its leaking some fluid, but nothing to worry about (yet). The fluid is very dark and sticky.

I am guessing that if this is setup anything like the rear window shade, this tube holds the length of whatever they use to operate the moonroof.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car