1972 Pearson 30 not water flowing through exhaust A4

[Jaa5]

Oberdorfer N202M was working fine, then without any warning signs, zero flow. Pulled pump cover, impeller looked OK. Put a new one in anyway, still no water leaving the pump. Inlet flow to pump is fine. With the cover off I bumped the engine and the impeller and shaft don't rotate! Removed the entire pump and see pin has sheared. What are the odds a new pin will solve my problems? And where can i purchase a pin? I can't locate one?
Thanks

[HOTFLASH]

Sheared pin

Of course need to figure out why it sheared.

[Jaa5]

right, my concern is what could have caused this? Is it possible it's just 47+ years of heat/cool cycles? It's not a solid pin (rolled-hollow) and did seem to have been putting some wear on the shaft slot as if it was too short, one end was partially worn down. Also, where did the pieces that sheared off go and do I need to be worried about them entering the oil flow at some point or worse. Should I just pop in a new pin and see what happens?