You may try replacing the o-ring but be sure to lube it first, with o-ring-safe lubricant (every pool store sells it). O-rings can rot out fast, even in a non-SWG pool if you don't lube them, especially before storing them for the winter.

Personally, I take a zip-lock, mark it with a Sharpie pen, then lube the o-ring and slide it in. Since I have about a dozen for all the quick-connects and ball-valves, I never have to guess which is which. I'm not a genius--I learned the hard way after I went to open my second season!