This valve dribbles and weeps for one reason: Because of gentle pushes up to get a small drain sample, followed by a gentle release down to the closed position. The remedy is quite simple. Whenever you take a sample, LOCK the valve in the open position. Then, when you're done, SNAP it smartly shut to the closed position.
The spring on my new one is very stiff so it really snaps back with a vengeance.
Locking it open for a healthy fuel sample (at least 1/2-1 pint, whilst rocking the wings) is something you should be doing anyway, before first flight of the day, and after last flight of the day, given the Sting's history of fuel tank delamination (and just various fiberglass debris and resin). Sump a pint mason jar full, hold it up to the sunlight, and swirl it in a circular motion. You'll be glad you're removing fiberglass gunk that won't then have a chance to make it to your gascolator, where it could result in fuel flow impairment.
I might be just lucky but the 15 gallons I drained were remarkable clean. No gunk in the filter when I refilled.
My method of installing was too tighten the valve slowly to around 80lbs of torque, the back off a half turn. Tighten to 80lbs again which usually got another 1/2 turn, the back off. Repeat until tight. This got to within a couple threads of all the way in.