We can figure out how to make the shut off valve not leak.
Here's the 8 sealing surfaces. First of
7:


And the
eighth sealing surface is the
rim on the bottom of the
tank.
The brass seals are reusable up until they get ring-scored. The torque to tighten the shut off valve is considerable (With 10" Crescent wrench type of leverage, and a 1" wrench on the flats to kep the banjo steady). I used
Seal-All® in Calif. gas in 2004, on all eight surfaces, and my valve did not leak. I would always turn my supply knob down to "
off" every time I parked the bike. I'll try Seal-All again, since I still have the same tube from 2000.
From a plumbing aspect, this valve and twin washer assembly is not used. The shut off valve is
a laminate-compression seal, I suppose, since there's no compression ferrule, just the brass (not very crushable) washer. If it were softer brass it would eventually tilt and throw the rod seating off
The first point of irregularities in an
aftermarket valve, would be the chromed surface of the
#1. shut off seat and then both sides of the chromed
banjo fitting, #6, #7. Most of the AM valves, seats and banjo seal surfaces are
slightly irregular and
chromed, so you can't really "deck" the banjo surfaces.
If you do, then it throws the rod alignment off, between the rod and seat. I've done it before. The rod becomes hard to turn because it's off center and doesn't want to seat any more. I ruined a banjo line trying to "improve" on the mating surfaces, and probably other people have done the same thing, and run to the alignment tool for a solution and that might not work.
What gasket will compress, not distort, and fill any irregularities in the valve seat and banjo surfaces

Delrin? PEEK

Although you can re-use the brass washers until they get ridged and that's a good feature, a lighter gauge disposable crush washer might work better.
Using Linkert
float bowl crush washers might affect the rod turning, since they'll be thicker when squashed.
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