I researched the problem. I found out on forums and from other Boxster owners emailing me that this was a common problem.
I called the dealer and the parts counter admitted going through a lot of cracked heads. The service counter on the other hand denied having more than one cracked head in years.
I called Porsche dismantlers. I spoke with independent service centers. They all admitted quickly that they had all seen a lot of cracked Boxster cylinder heads.
So what was Porsche doing about this?  Their solution is to replace the entire engine (about $13,000 USD) and not admit that there is any problem. Of course, I wanted to fix this thing myself, but found out that the new head, special tools and other necessary parts were practically the cost of a  replacement engine.