My vote would have been valve seals as the symptoms are classic. I replaced valve seals on countless Chrysler mini vans with the Mitsu 3.0. It is possible to damage the seals during install, either by carelessly jamming the seal over the stem or using a too small driver that damages the seal top. I'd look for other sources of oil first though.

This engine might have a problem with the venting baffles in the valve cover clogging up. There might have been a post on this site with a fix.

In any event, please post the results so others can benefit.