I'd say if it concerns you and you can have downtime on this car (and want to keep that slant six in there for a long time), you could pull it out, clean everything up, install all new gaskets, paint it and the engine bay and then drop it back in. I like doing this myself since it makes everything look nicer and gives you piece of mind.

I would spray that Casto Purple engine cleaner on the engine and engine bay(be careful not to get it on your exterior paint), being sure to keep it wet with the stuff every 5 minutes or so for over an hour, scrub the stubborn stuff around with a brush, and then blast it clean with the water hose.

Dry the thing out, change the valve cover gasket being sure to use the black, non-cork type gasket glued to the valve cover with Permatex ultra seal after straighting out and flattening any warped/pulled down bolt holes etc). Don't use any permatex on the head side of the gasket, but do use a thin coat of clean oil.

Adjust the valves while you have it apart. Best way on these is to do it with it running at low rpm. (search Slantsix.org for info on this technique).

If the oil/goo seepage comes back, you can always dig deeper into it, and your fresh valve cover gasket will still be attached to your valve cover, which can come off and on many times without damaging the gasket if necesary.

That's what I would do, but do what you want and post some pictures of your progress.