Geez rjn... You describe piston ring blowby! Take the grommets out of the cover holes and see how much smoke comes out when hot and running. Pressure inside the engine is from the rings...not valves. Good you got it not to leak at the cover.. But now the problem seems to not have been the cover after all.
I am not rereading posts to see but what do you know about this engine? If new it might just need running some to breakin the rings till they are seated good. If old and used...oh shucks! Or what about the pcv system? Is it clean and fully functional? Smoke from the dipstick hole is a hint of too much pressure inside the engine and the pcv system should gobble up that pressure.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />