"Hi Marc. Thanks for posting all that, it is very helpful for potential or current owners.
If the blue smoke goes away and it always does that, then I'd agree, do nothing. Robert though, has said that his is getting worse over a relatively short period, which I would be concerned about. I suspect his may be injectors or pump as well as the seemingly common blue smoke at startup. Maybe it is also a symptom of the timing belt being worn as well based on his mechanics comments on pump timing.
Wild personal theory time [img][/img] --- (The blue smoke at startup issue is very likely oil sitting around the valve guide(s) after shut down being drawn down into the inlet valve induction area as the engine cools. Off the top of my head, a fix may be to manufacture a small sleeve to light press fit over the top of the valve guide to raise its height above any pool of oil that may be sitting there.) ---
As you rightly suggest though, as a choice, I'd defintitely steer clear of this engine for a boat. My poor old 4.236U's might be hard to get some parts for, but then they hardly need any... ;)"