Stopcock weeping

[john2k]

My home was a newbuild around 15ish years now and under the kitchen sink is one of those brass stopcocks labelled main water stopcock. It’s been fine all these years but recently I had to turned the water supply off and on a few times to do some bathroom work. Since then I’ve noticed that the stopcock seems to be weeping water. I’ve put a little container under it for now as I’m still going to have to turn it off and on a few more times. But wondering is this normal for this to start leaking when it’s used? Is it matter of maybe just tightening the top nut ? Below is a pic of the type of stopcock I have

 

[denso13]

Is it matter of maybe just tightening the top nut ?

Yes, try that first.

 

[Dereekoo]

And if that does not work open the stopcock to fully open and see if that stops the drip. If that does not work then undo the top nut, slide the body up the spindle and then either wrap 6 turns of PTFE loosely around the spindle and then retighten the top nut forcing the PTFE down into the stopcock body, or instead of PTFE go old fashioned and wrap 4 or 5 turns of suitably sized string that you have waxed by rubbing it with a candle around the spindle and as per PTFE tighten top nut and force it down into the stuffing box, If that doesn't work get a new valve.