I realize this thread is old but I have helpful information if the engine in the FG25ST-11 happens to be a Nissan H-20.
There was a problem in the casting of that engine bell housing (adapter) that neither Komatsu nor Nissan ever really admitted to, which would result in exactly the type of failure reported by the OP. Replacing the bell housing with the same OEM part number would just get you another copy of the same weak casting which might also break later.
The "cure" for the problem is to purchase a bell housing that Nissan made for the later H-20 Stage II engine (which appeared in the Komatsu FG--ST-12 models.
The later casting was stronger and to my knowledge never had any breakage complaints.
But if you do use the later bell housing on an older engine you will have to fabricate a mounting bracket for the ignition coil.
The coil mounting was cast into the bell housing on the H-20 engine (separate coil and distributor) but the H-20 II had the coil incorporated inside the distributor so Nissan deleted the coil mounting provision from the H-20 II casting.
H-20 Stage II bell housing Nissan part number is 12320-K9302

are they dropping them off the dock? Do they have a rough interior? Sounds to me that these trucks are being abused.