Bruce, if it makes a difference, I can't find any reason to replace the IKH27's until 200+ hours. It's typically been every other annual, but given how little I've been traveling recently, it might turn into three or even four years.
This 213 hours. The ground electrode has lost material near the tip, on the side facing the center electrode, which has eroded hardly at all. The result was increased gap, but no difference in operation. They could have been re-gapped and run more.