I've been using Grolsch bottles for ages and they just keep on giving. Replace the seals when they feel a bit soft or floppy (e.g. http://rover.ebay.com/rover/1/705-53470-19255-0/1?icep_ff3=2&toolid=10001&campid=5338413729&icep_item=223303828565 ) and they'll be good for years to come.
