i just bough this car a few weeks ago and noticed a small oil leak at the left corner of the exhaust manifold. I found that one of the scres was loose. So, I replaced the exhaust head gasket and the flange gasket as well. also, i added an oil stop treatment to stop the leak. It stoped for a while, however i still get some oil at the exhaust manifold sometimes. It usually happens during initial turn on only, and after that the car is fine, super. what could be the cause of my problem?