also, maybe a long shot but i had a similar'ish problem and i couldnt figure out what it was. after much head scratching i decided to take the cam cover off; some idiot had put the cam cap studs in upside down which meant the nipple of the stud was pressing against the cam cover which stop it sealing properly.

worth a shot for the sake of 20 cam cover screws

edited to say: the cam cover studs should be input so the nipple of the stud goes into the head rather than the other way up.

having said all that i dont think it would cause oil to come up the dipstick, but worth a shot