At least on my BMG copy has nearly 2mm gap between the secondary gear and extruder body (see the picture). This allows the filament load failure if tip of the filament is even a bit wrong way curved.

This add on piece fills up the gap allowing filament to go nowhere but rigth. The piece can be glue with cyanoacrylate.

-Place filament (bit of oil avoids the filament stick with the extruder :-)
-Glue the piece in to extruder body so that the filament travels through the slot. Long section towards front wall