the dip stick seats into the block, not the oil pan. with it fully engaged, the little lip around the bottom of the dipstick should be flush with the block, or at least really really close.
I ran my motor initially when I first finished my rebuild, and didn't have the dipstick in at all. oooops, guess I forgot that part. but no oil spilled out at all. However, I didn't take the car on a drive that way, so maybe taking corners would force some oil out the hole.
Black RTV should work against oil, but if the tube is fully seated, the only place it could be leaking oil would be from a crack in the tube itself, assuming it's even comming from the dip stick.
I would pull the tube out completely (be warned, putting it back in with everything else on the motor is a bit ackward)
and then check for cracks in the tube.