Well, you ain't gonna wanna hear it, but the "correct way" that comes apart and goes back together is to remove the oil pan, clean it all up GOOD, put the timing cover on FIRST, then the oil pan. That's how they are "supposed" to be assembled. I know a lot of people remove and replace the timing cover itself all the time, but you risk exactly what you are experiencing. Also, sometimes, that front rail on the oil pan does get bent down and upon retightening, does not compress that front rubber gasket enough to make a good seal. The only thing that will correct that is, once again, removing the oil pan and bending that rail back up in the correct position and reinstalling everything correctly.