I just changed my oil with Royal Purple and a Ford Motorcraft oil filter and it leaks from between the gasket and the block. I lubed the gasket prior to install and hand tightened. Started the engine and let idle for a minute with no leaks. Took it for a test drive, came back and checked and its leaking a little. I tryed to hand tightened it again but its on there, wont move, so now what? I ran the engine again at idle, checked, no leak. Reved the motor for a minute, checked, no leak. Went to the store, came back and checked, Its leaking again? What is going on?