[Richard and Rhonda]

If you are talking about the push on style fittings, I have notice that with time the mechanism inside the fitting forms a ring on the outside of the piping. This causes it to leak if the pipe sometimes. My experience is that the problem is the tubing and not the fitting. You may find differently

I have used two solutions. The quick and dirty is to cut off one half inch of the pipe and stick it back in the fitting. If you don't have any pipe to spare, I have used something like a center punch pushed into the pipe to expand it slightly, then I stick it back into the fitting. This works a lot better than you would guess.

Don't waste your time with any type of sealant and the push on fittings. You will just make the leak worse, and most likely ruin the fitting from ever working properly.

But the hard core engineer in me, replaces the leaking fittings with a true compression fitting. The one with a brass insert and a nut that tightens down around that.