Usually, oily spark plugs in these engines is coming from piston rings(s). You may have good compression/blow-by values but problem propably lies on oil ring(s), not in compression rings only. Valve guides may be worn, but especially on O-200 you will start having another problems very soon. (sticky valves) You may also have rotated rings, and gaps are parked on lower side of the piston circumference but this also greates bigger compression lost if all of them are in bad position.
Need to remember that Continental valve guides are located higher than oil supply, oil is coming via pushrods and directed to valve head and rocker axles. Guides are hiding behind valve spring and its retainer, so oil is not flowing over them directly. There is oil mist and oil everywhere under rocker covers but guides are located in fairly "dry"-ish area.