Oil Leak

Tom the O-ring does not seat against the block nor is there any gasket used to seal the dist. The O-ring seats into a groove on the dist. housing and when the dist. is installed the O-ring ends up down inside the block a little so there's no possible way the crack or broken chunk in that picture can cause a leak at the dist. unless it's broken completely through the block, which it doesn't look like it is. I apparently didn't catch the issue involving the oil pump driveshaft but it sounds like you had to replace it. If it is too long it can hold the dist. up so that the O-ring is not seating down in the block.

I attached a picture of a dist. I sold a while back. It's not a close up of the O-ring but if you look closely you can see the O-ring seats into a groove.

Numerous time in the past I've seen the dist. blamed for leaking when it was actually a leaking oil sender unit. It's right next to the dist. so if it leaks oil ends up in the same area. You might want to check that.