I have a brand new gas tank,brand new sending unit in a 69 Charger,and it's leaking by the sending unit.Is this a known problem for B body cars? Is there anything I can do to solve this problem? The retainer is tight and the gasket seal is new,and still seaps out,even if the gas tank isn't full.

You don't want to hear this, but I would drain the tank, remove the tank, then remove the sending unit and replace the gasket. You must have pinched it when you first installed it. Do not over tighten the retainer ring when you re-install it.
Good luck

hey, my e-body sending unit can wiggle(a little) with the ring tightened all the way.

also the gas gauge likes to hang around 1/2 full...even when full.

are these common ?

Check to see if the retainer is put on flush to the tank ( I know you probably did this already),or you may have pinched the gasket when installing it. If your using the retainer that came with the tank--throw it away & buy one from a mopar performance dealer. I've had two tanks leak,changed the retainer & zero problems now. If you compare the two retainers, the one that comes with the tank it is slightly THINNER than a mopar performance one. If I remember right I got mine from Mancinni.

I used a new mopar seal and the old retainer on my tank. The retainer that came with the tank was too flimsy. Mike

Thanks Guys,I just placed an order for a new seal and nos retainer.I'll see how that works.