Well i have not had your problem so i dont know exactly what it is but i think if you remove that headliner you will be able to see exactly what is wrong because it exposes everything inside the roof. The motor sounds like it is fine as long as it is making a noise, if it is overly loud i would think that maybe the cable is broken or the clutch is broken. You can get to the clutch by removing the plastic covering on the back left hand side of the trunk, where the motor is.

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Pete

1986 Euro Black Metallic 190E 2.3 16V