Whenever an engine is running, there is vacuum pressure. Lots of vacuum after the throttle is lifted and nominal when throttle is applied. Without vacuum, your car would not run. Enough said.

The oil breather system uses vacuum to get the oil fumes out of the crankcase and routed to the intake for burning, rather than just letting the fumes escape into the atmosphere. So the oil would not come "out" of those lines.

When the dealer replaced the oil separator box, did you get billed for various hoses or were the old ones reused? Specifically the one hose from the oil filler cap to the separator box.
You might want to remove the cover over the spark plugs and check that the hose did not come off and is snug.

When you said that there is oil everywhere, does it concentrate more in one area than another? Like the front of the engine, pass side, drivers side, etc? Could it be a leaky line at the radiator?

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)