I know I am new here but have turned a wrench for a number of years. I have seen this same question come up on about every kind of engine and the answer always varies according to the manufacturer. If I cannot find specific information and also as a force of habit, if I am installing the old head bolts oiled or not I always clean the bolts on the wire brush on my grinder and when possible I run a tap in the bolt hole to clean it out. Hey, it works for me!