2000 XJ 4.0 Oil pump drive shaft seized

Some weeks ago my XJ stalled, 3 or 4 restarts, then only cranking, no start.

I was prepared to replace the crankshaft sensor, only checking the camshaft sensor to miss anything. Found that the oil pump drive shaft lost 3 teeth.
The shaft was completely seized in the housing.

The camshaft looked OK. After replacing the unit, the XJ is running fine as ever.
Any reasons that caused this? How is the shaft lubricated?

Thank you.

The pump drive has a oil impregnated bushing and get a little additional lubrication from splash.

I've had this happen also. You can, in an emergency, drive the drive out, clean and lube, and replace the gear from a distributor, but new ones are cheap enough these days to not be worth the work.

Someone on here built a dedicated oil jet to add more directed lubrication, but I can't remember who it was.