fouled plugs

TrailBeast said

Agreed.

One other thought would be a mismatched intake to the heads sucking oil past the gasket.

Just saw the headers post, sorry.

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this may be your problem since it's all on one side or at least the gasket didn't seal. remove the intake and have a look see. oil can come up from the valley under the steel shim gasket real easy, use plenty of glue.