If enough of the seals are letting oil get down them then yes, oil will be seen getting up into the intake runners and after you shut down a warmed up motor can be seen pooling on the back side of closed intake valves.
This is assuming you have leaky intake seals.
Even leaky enough exh valve seals can do this.
With either or a combo of both of these conditions to the point you have it occurring at you should be seeing blue oil smoke puffing at idle and you should be picking up a oil film on your finger if you run it around inside your tail pipe’s.
It could be you are sucking oil in from the intake gaskets as you questioned, but you would also at the same time be having a vacuum leak.
Has the way the motor idles changed lately?
You really need to find out what’s taking place here because oil getting into the chambers will greatly cut down on a fuels level of octane.
I have never used sealer on these type of F-P gaskets when everything mates up like it should other then a smear around the water cross over if I have separated it.
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