Exactly how serious is a hairline crack at the wastegate hole?
probably not of much concern really. the turbo on my mitsu is known for cracking the exaust side and had some prettty decent cracks in it... going thru both sides of the waste gate and further down into the turbo yet spooled fine and such until one of the oil seals let go.
I run several turbos that had several small cracks around the wastegate hole. I posted up picks on Tuboford, they all said that I had a very good housing. LOL
It's typical and probably something you will never even notice.