i have just replaced the valve cover gasket for the 2nd time in 6 months. upon removing the old on this time i noticed the person who did the last installation did get all of the old and very hard gasket off. i removed that piece but the leaks seems worse. i have a new oil sending unit but have not installed it yet? 2nd problem is my coolant is disappearing but i can find not visible leaks? any ideas on the possible solutions.