Yes they are sintered steel, one common reason for failure is that to remove or install them typically something is pried against the spoke. If it leaves an indents or marks that can provide a starting point for stress fractures. 5M pullies are commonly uses as they have round holes rather than spokes and are not susceptible to fracturing. Gordon on SF made a few utilizing an aftermarket CV which also added a bit of overdrive. our belts have a bit of a unique tooth profile so sourcing something is not the easiest.Can you cnc machine a new billet steel oil pump drive pulley?
Any experience case hardening the teeth profile area for the belt?
Possibly undersized for increasing the oil output?
On the failed part can you tell from the fractured surface what type of material they used for it?