mine done the same thing, the head bolt hole is also a drilling for a oil passage. it is considered normal. but if you want to stop it all you have to do is remove the bolt. clean the threads and the hole with brake kleen, dry with compressed air. and put a small amount of blue silicoln on the threads of the bolt and reinstall. thats what i done to mine and it worked wonderfully!! pretty easy job, be sure to retorque the headbolt to factory specs!!!

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matt