KUDOS to robertop for the correct answer. Straight out of Strengths of Materials.

I have never bought a new head bolt and as they are inside the engine I haven't seen any that were corroded badly. Oily, yes.

If you have a few thousands invested in an engine it is nice to spend a few dollar$ and have new bolts. But on a 318? only if you are running forced induction or something like that.

R.