Brand new motor installed not yet fired. Filled it with oil and got a slow leak between the the bell housing and the dust cover. Not trans fluid its the 10 W 30. Is the rear main no good? What could cause this? I don't want to fire the motor and blow a seal. Any ideas?

 

Might be a rear main. Might be the oil pan gasket. Usually leaks back there happen when the motor is running becuase the oil level isn't high enough to just run out of the back of the motor without the crank whipping the oil around. Yank the 6 bolts from the dust cover and have a look.