Intake manifold gasket... I don't know how it could cause blue puffing, to be honest. A vacuum leak will cause funny things to happen with the idle and all that, as you've guessed, but LH2.4 should compensate for much of that. Any other explanation I can dream up using the intake gasket seems less and less likely.
While you've got your intake manifold off have a look at your valves. If one or more are wet & gooey, that tells a story. It's not a guarantee, but it's more information. If they all look clean, the problem could be downstream of your intake valves, but port fuel injectors do a great job at keeping valves washed clean. If one is gooey and the others are clean, it could be a valve guide seal or it could be the injector is not spraying well. If all are gooey it could be that all your guide seals are leaking a little or it could be your turbo or PCV are introducing oil into the intake. If it's your turbo, your intercooler will probably be full of oil - check that. There will probably be SOME oil/water in there anyway, turbos do that. If you've got access to a leakdown tester you can check the health of your rings. This isn't a guarantee that you're leaking oil past them, but it's a safe bet. Your turbo could also be pushing oil into the exhaust, but that'll normally happen under more load than just idle. Pulling the downpipe off might show you a slimy turbine, it might not.
Puffing oil after an extended idle is most commonly intake valve guide seals. You've probably nailed your problem right there. It's not a new engine, it may be something you have to live with unless it's a lot worse than I remember (I don't remember Dale's car puffing except for very occasionally).
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