The Stanley flask you have should have a lifetime warranty, try contacting the Stanley uk agents & they'll probably send you a new one if you send them your old one. But be warned - those flasks are rubbish, after a while they stop working,
I have one & it only gets used 2 or 3 days a month but I'm on my third one in 5 years after the first 2 failed! On the other hand I still have the Thermos stainless steel flask from my school days & it still works perfectly over 30 years later!
All I want is one that doesn't leak.....the stopper is useless. I've replaced the original with a genuine Stanley spare which I got online but that was just as bad. I'm going to shy away from Stanley and try something else. I spotted a Thermos brand metal flask in Tesco yesterday but again the stopper looked very cheap and the flask itself was a made in China item, certainly not a quality looking item........the quest continues......