i have a 97 freightliner fl60 5.9/allison.it had leakage on top of the engine,i assumed it was valvecover gaskets,so last week i changed em,they weren't hard and were pretty flexible.anyway dried everything off and today i put about 30 miles on it and i got that leak again.it is mainly between the 1st and 2nd valvecover and the 5th and 6th.but it really appears to be coming from the little softplugs on top of the head.is this a typical problem??