On my 300D, it is the little white knob that twists up near the IP. Mine is broken right on the little portion that is threaded. I was hoping it can be repaired or whether I will need to replace the entire unit.

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1960 MB 190Db w/ full sunroof
1985 Toyota Pickup
2006 Honda Odyssey EXL R&N
2001 VW Jetta GLS TDI