I wanted to follow up on this thread as I may have given some misleading info:
There was an o-ring in the housing where my dipstick plugs into the pan, and it was damaged, but I don't think it is original to the engine. What I now believe is that the P/O put the o-ring in to stop the leak. The leak was caused by the presence of too much crankcase pressure due to excessive blowby, a side-effect of worn rings. As much as I had hoped to solve it with pcv valves, and stopping leaks, the bottom line is that the engine needed a rebuild. If you have this problem, you can probably stop this leak, but the excessive pressure is going to cause another gasket to blow and a new leak. Unfortunately the reality is, it is time to rebuild.
I rebuilt last week, and replaced the dipstick with no o-ring and I now have no leak.