Just musing on this problem, may not be applicable...
In my case I determined that the VERY clean plug was a result of water in the combustion chamber, that has a tendancy to cut carbon and clean the chamber in general. I found what I thought was a bit of moisture as I cranked the engine over and felt, sniffed, inspected the compression gases being pushed out the empty spark plug hole, which led to the conclusion, blown head gasket.
Of course I changed the
oil, but I've always wondered, is it possible that compression gases were going into the water jacket when I was driving "hard" but that no water was actually getting into the
oil? Perhaps a small amount in the combustion chamber, not enough to really show itself, other than a "hunch" and a super clean plug.
Perhaps a blown head gasket doesn't always mean water in the
oil? Is the question.