Under the seat in front there is this bowden cable which adjusts the seat belt height in the B-pillar depending on the movement of the seat base. Many have lost the pin which secures the bowden cable under the seat when they had the seat out. Then they searched in the ETK for such securing clip and found a strange thing in the E32 and E34 ETK for this, a white plastic clip, actually the white plastic clip is used in the doorlock system., click on the pic #18 Halteklammer / holding clip 51211976597

The correct part made of metal you can find in the ETK for E39 and E38, p/n 72118185136 , looks like this https://a.d-cd.net/9a075dcs-960.jpg and should fit E34 and E32. There seems to be a wrong info in the ETK.