[Luccia at Pelican Parts]

Is it the belt or the unit that the belt clicks into that is getting stuck? This article should help a bit with the seat belt removal: BMW E90 Seat Removal and Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article.

Here is the upper seat belt section: Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI
or,
Here is the Seat Belt Receptacle with Belt Tensioner: Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI