the last two "bleeders" i've messed with were the back corner of the passenger side valve cover. a friend of mine has a 383 4spd car and oil was covering the tranny and exhaust. we actually took the gear box out a couple of times to re-seal it. in a final act of desperation i checked the valve cover bolts and the back corner bolt on the passenger side was loose. tightened it up and bingo no leak. i had a nuisance leak on the 440 in my '65 coronet. nothing serious but suspected it was coming from the back of the oil pan. i was planning to yank the engine and fix it but in the last final act of desperation i tightened up the passenger side valve cover; leak gone. sometimes the leak is never where you suspect it.