Just swapped in a b18b and after connecting the fuel line from the filter to the rail, I still have a small leak. The leak is nearly invisible when priming, its just when pressure is in the rail for a while there is a small accumulation of fuel underneath the half sphere where the fuel line hides in the rail.
I have used new washers supplied via a new fuel filter with no luck.

In the arrangement I have it.... Large nut>new washer>fuel line>new washer>end of rail..... the leak is between the last washer, fuel line, and end of the rail.
The front portion containing the large nut, washer, and fuel line is perfectly dry with no leaks at all.

Unfortunately the back portion of this seal between the fuel line and the washer is hidden away in its little half sphere portion, therefore I cannot put teflon tape between the surfaces to fix the leak.
I have also tried this with the old washers and no luck....do you guys usually use 2 washers or something as I have no idea and I don't want to shear off the large nut off the rail.

 

I fixed the issue. The problem is that I initially used the brass washers provided, however they are almost 1mm thinner than the stock silver ones. I cleaned up the old washers and put a very small layer of high temp thread sealant(white) on the surfaces. On the thread I also put a small amount. Combined with the better seal through the sealant and tighter clamping from the larger washers, there are no more leaks.