Crack in engine case...

[skymstr02]

Sounds like you have a light case, unfortunately that is a common problem on the light cases.

In many cases, the cracks are acceptable if they are monitored for progression.

In your case, this may not be possible with the loss of oil pressure. This indicates oil pressure from an oil gallery is leaking internally into the case (think bleeding internally). This is not usually repairable. The oil gallery may become obstructed if the crack is weld repaired.