I had a question very similar to this that should provide you with some of the answers you need. See this thread:
What Tap to Clean Head Stud Holes?
Basically, the tap your machinist used was probably a cutting vs. cleaning tap and opened it up a little. I did a similar thing on my case. One out of 24 is probably ok, though this is the 1st engine rebuild for me.
Best regards,
Michael
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Michael
'82 Euro SC 'Track Rat' 22/29 Hollows, 22/22 Tarrets, Full ERPB F/R, Rennline Tri Brace, Glass bumpers, Pro 2000's, 5 pts, blah blah blah
'13 Cayenne GTS