Whiteish crud is usually from water mixed in with the oil. Water is there because the engine oil doesn't get hot enough to evaporate it off, ie. short trips at low rpm.

There wasn't any oil on the dipstick????? Have you cleaned the flame trap lately, especially the small hose going to it? Throw away the round screen inside the flame trap.

The oil separator could be very dirty by now, but that means you need to remove the intake manifold to gain access.

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