Hi All,
The rear seat belt buckle holder (the one in the center of the back seat rest (52201941338 Lower belt catch support) is unobtanium.
I am missing mine and I have just redone my leather seats.
I took my chances and ordered a regular double seat buckle holder (72111904867, 72111904865) and I am happy to report that while it is not perfect, it can be made to fit.
The pins on the back are really just thin rods, instead of the pine-tree looking fittings, but you can either glue it in, put washers on the pins, or drill them through and put some nice countersunk 6mm bolts in there (which is what I did).
It may (or may not) help someone some day.

The rear seat belt buckle holder (the one in the center of the back seat rest (52201941338 Lower belt catch support) is unobtanium.
I am missing mine and I have just redone my leather seats.
I took my chances and ordered a regular double seat buckle holder (72111904867, 72111904865) and I am happy to report that while it is not perfect, it can be made to fit.
The pins on the back are really just thin rods, instead of the pine-tree looking fittings, but you can either glue it in, put washers on the pins, or drill them through and put some nice countersunk 6mm bolts in there (which is what I did).
It may (or may not) help someone some day.