Common problem with these roofs.
Because of the size of them, the front roof has very long tilt runners out of necessity.

To minimise intrusion, they are also thin and light + heavy glass roof = break easily with regular use. (My E39 has similar issues)

BMW here will only replace the cassette at around $7K including labour.

You may be able to find a specialist who can get the part seperately and dissasemble your roof and replace it.

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Black is the new Black.