I agree, Classwife. Give HOH a call. An occasional problem coil is a lot different than several. Also, I've never had a dud coil, though I have heard it does occur.
My guess is that one time the coil cross threaded a bit and some metal shavings might be hiding in there as the kabuki steel is stronger than the coil thread metal. Some have suggested using gun cleaning brushes on the threads once and awhile. HOH will be happy to check it out for you, clean or fix if needed.
Nauti's and Nauti mini's are available at lots of vendors. As I am stocked on them, I don't know who has the best deal right now. Most anywhere coils are sold, will have them. I do think it a good idea to have one in your arsenal, even if just to test the coil.