I have a water shutoff valve that has one end into a plastic pipe that is coming from mains and another end is going into the faucet.
There was never a leakage from this until recently when I had to close and open shutoff valve few times. Probably this was first time it was done in years and therefore this valve started to leak.
In the picture, the shutoff valve is the one on the left tube. The leak is from the nut that is below the white plastic.
The leak is very minute, it is 2 drops per hour may be. It is coming from the lower nut that is attached to the plastic tube. I have tried to tighten the nut but I backed off when i heard a plastic crack sound coming (who uses plastic pipes?).