I don't have any Korinek's in my family tree.I was looking for Kornaus which I found isn't on GenForum.I went to school with a Robin Korinek and that is what sidetracked me.
To find the name of your g grandfather here is what I would do:Order a copy of the SS-5 form your grandfather filled out.It's pricey at $27 but to get a parents name (esp mother's maiden name!), it's sometimes worth it.I would also try to make a guess as to where your Korinek family might have been living in, lets say 1910 or 1920, and check out a census index for that state and that surname.I don't know if you've tried these avenues yet.
Please let me know of your progress.Good luck!!!