351w Water Pump Leak - Void in the casting - how common is this one?

[RRussellTx]

I've been fighting a water pump leak on my 351w for a couple of months now and I finally found the culprit.

The problem started when I swapped out my water pump to accommodate my new pulley kit and Power Steering Pump (I needed a 'Clevor' style water pump to accommodate the bracket mounts).
Every time I installed the water pump, there was a small leak from the inside bolt hole on the driver side port - after the engine came up to temp (and pressure). At first, I just thought I had done something wrong in the installation process - even though I was very careful. I wound up draining and reinstalling it 3 times with greater and greater care each time. I did closely inspect the water pump each time to see if I could figure out where it was leaking from but without any obvious clues.

Finally, I broke down and purchased another new water pump and installed it without any leaks. 4th time was the charm...
Frustrated, I drilled out the offending bolt hole one size and noticed a small crack on the casting.
I drilled it out another size and the crack grew even larger as you can see in the image below.

All of the draining of antifreeze and scraping of gaskets really had me down and doubting my mechanical skills so I was very happy to realize that the issue was not the quality of my work!
This project is all about having fun so I wound up letting it sit for a few weeks here and there while I gathered the patience to do it again.
Now that this is resolved I can move on to the next adventure!

Hopefully this post helps someone else if they run into a similar issue...