Not wanting to dissappoint I'll take on the comment that the OEM fuel valves are crap.
In fact they're not and no worse then other valves. A tapered self sealing nylon cone in the valve body makes complete sense; until the in-tank fuel filter is removed. Many removed the filter due to it getting plugged with rust and the fragile element being damaged in attempts to clean it. The rust, a result of age, then requires the tank to be cleaned and sealed but typically the damage to the fuel valve has already been done. With no means of an external filter being fitted between the tank and valve an internal filter is required and should be for any fuel system that has the fuel valve attattached to the tank.
It would likely not make any difference whether the valve cone was made of any other material. The rust particles will grind any surface and that scoring is what makes the valve leak fuel into the carbs. A single O-ring behind the face plate ensures no exterior leaks.
Depending on how bad the scoring is on the cone and bore, there is a good chance this damage can be removed and the valve made leak proof. I've repaired 3 valves by lapping the cone into the bore. All 3 repairs were successful - no leaks or weeping.
It's not a crappy design. It's a lack of understanding of what not having an internal filter does, down-stream.