I would guess its worth $37-38k...
I've been following these for a bit and it appears they have had their initial big depreciation drop with the intro of the new 3 series... kind of sad, but I don't think there is enough of an enthusiast market to keep the used diesel prices where they should be.
If you find the right person you might get $40k
Rover - 2013 Holden Commodore SV6 Sedan
Clark - 2013 Holden Commodore Sport SV6 Wagon