Hi Axel,
in my database Hakutetsu maru #13 was torpedoed and sunk by USS Drum at about 1400 hrs of 8/9/43 in position 02.30 S, 141.44 E.

In IJN monograph #116, however, there are 2 Hakutetsu #13 listed, both being sunk the same day, this one and another one at Naha, Okinawa.

Evidently we are dealing with a duplication, since the tonnage is identical. Given the more accurate research which has been done on US sub attacks, I tend to believe she was lost to an attack by Drum.
Regards, Brian