I'm trying to be vaguely green and continue using an old aluminium drinks bottle I've had for ages but the gasket around the stopper is getting a bit hanging... does anyone know where you can get a replacement seal/gasket? It seems they must all have been created by one ancient artisan in the depths of darkest Peru a thousand years ago or something - you'd think they'd be easy to replace but no. Apparently not. It appears to be silicone, 3mm thick, off-white colour (or it was before it got stained black and brown), 34mm od, 30mm id.