Found the leak
My partner and a buddy fixed the leak. After cleaning off the oil, running the engine to find the drip, they discovered a hole (drilled like it was supposed to be there) that had the plug partially missing.
The theory is either a freeze plug or, since these are marinized Kubota tractor engines, it was a hole not needed for marine use.
They scrubbed the area clean, applied two layers of JB Weld and we no longer have a leak!