The upper/lower intake manifold gaskets have no oil ports because there are no components in these areas that need lubrication. So this can’t cause oil contamination in the coolant. Only coolant contamination in the oil.
If there’s indeed oil contamination in the coolant, I would look more towards a leaking transmission fluid cooler in the radiator. Because when an engine overheats, the transmission also overheats along with the tranny fluid. And this can be enough to cause the tranny cooler in the radiator to crack.
Tester