I just bought an '84 westy with a similar problem.  When you fill it up, 
fuel spills out on the drivers's side of the van!  The previous owner 
showed me the cause:  There are two overflow tanks, one of either side of 
the main tank.  (each holds maybe a pint, very small)  There is a hose, 
similar to VW vacuum hose, connecting them.  In my case, a T connector 
had broken, causing the leak.  I haven't fixed it yet, since there is no 
point in it until I get the heads back on, but it seems easy enough.

Bill