I just ordered a new flange from www.worldimpex.com for $9 recently... it comes with the new o-ring. If seems to be common for the flange to crack and for the o-ring to "go bad"... I guess it gets hard or shrinks or something. If you're just being really cheap, you could take the flange off, remove the o-ring and take it to your FLAPS. They can go through their thermostat gasket box and find an o-ring to match it.