Hi Adam P. in Charleston.  I had this same problem in September with my
'81---The tank filler tube must be in exactly the right angle---I mean
exactly!!!---or gas will gush out.  It took looking at my other '81 to copy
the angle exactly.  This process took me one day because I did not look at
the non-leaking tube first.  It will leak if it is just a teensy bit out of
angle.  The large band clamp at the upper end must be loose to do this
adjustment.  Once you get the angle right, assuming there is gas in the tank
and it is leaking out all over your driveway as you do the adjusting, it is
hard to tell that you have been  successful  because the gasket will still
appear wet and gas will still be dripping from the underside of the van for
a few minutes.  I had a very large fan blowing on me for safety and to dry
things off quickly.....
Good luck with this!  And, have a Merry Christmas!

Regards,

Michael and Christina Nichols
Atlanta, Ga.
2--'81's