Chuck, I'm curious to know how old was the raw water cooled manifold,
and how many hours were on it. Is there any rule of thumb for
replacement of these things?



AFAIK, the manifold was original.

I had it removed and inspected a couple of years ago, and specifically inquired
whether I should consider replacing it. I was told, "No, it looks fine. I
wouldn't worry about this manifold at all."

Had I to do over again, I would have simply replaced the manifold at the time I
was concerned about it due to age, when it was about 15 years old. These
manifolds are $$BIG and I went the cheapie route. Paying for it now. :-(

Rule of thumb? Replace *before* failure. :-)