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I think you are asking if there's an o-ring where the tube goes into the block. I don't know as all the ones I've seen as well as those in the parts catalog I have go into the pan.
The dipstick tube has a "lip" where the tube sets in the block...I believe it's slightly tapered below that where it fits into the block. It's a press fit and probably has an "O" ring there. Going from memory here and it's not as good as it once was....sounds like a Country song?....."I'm not good as I once was, but as good once as I ever was." Hahaha
I have never seen an O-ring on one of the tubes. If it is leaking it has probably been worn down or crushed. Put some RTV around it under the crimp. That should stop your leak .
Intake manifold maybe. I'd clean it off real good and then watch it closely to see where it's coming from. Make sure your PCV system is functioning. I've been known to restrict the intake air to the PCV in order to create a slight vacuum in the crankcase. Tends to suck in oil leaks and help idle quality.