if your "curve" is new, contact the manufacturer, inform them of the defect and request a replacement. they're a reputable company and i suspect they'd be happy to send you a couple new rings. as for your original question...alternatives for the curve...i have/wear a CB-3000. it's somewhat smaller than the curve, but notably more comfy than the original -2000. i actually wish i'd bought the curve, as i'm a bit large for my -3000, but, well, it's okay. i dont' mind being a bit squished.
if you DO opt to try the -3000, i think you can purchase just the "receiving" tube (saves some $$$) and use the original O-rings, pins, spacers, etc. with it.
best of luck to you.