390 rear main seal

Hi i have a 66 390 that i have rebuilt to put in my 66 comet i filled up the engine wih oil befor i put the engine in the car, as we had the engine up on the cherry picker with the the engine tilted back we noticed that we had a little oil on the flexplate running down , is the rear main seal leaking ? as i put it in new, i may have put it in wrong by mistake ?
Thanks
Mike