Sorry about your bad experience with the Grolsch bottles, Arachnyd. I noticed you mentioned that you had changed the rubber seals before you used them. I wonder if that may have been part of the problem? I have been using mine for a long time with little problem. Perhaps if my beer sat around for a longer time I would also find that I have the same problem with gas escaping. I cycle through a batch every four to eight weeks.
I left the original rubber seal that came with the bottle, on. It may be a factor. It may be that the seal has an exact tolerance, a balance between elasticity and thickness that is Grolsch bottle specific, Grolsch seals will only work on Grolsch bottles?? What kind of seal did you use? I have about eighty bottles, some from the early ninetys and even earlier. I've noticed that some of the seals are developing small cracks and I suppose I should be replacing them. Still, they seem to be working.
I wash my bottles by hand with hot soapy water and use a bottle brush to scrub out any bits that may have found a home in the bottle. I avoid harsh detergents and bleaches, if possible. This helps, I think, with keeping the integrity of the rubber seal intact.
Another thing is storage. I have a cold room that rarley ever gets above 65 F(17 C) and usually is much cooler. Gas expands when heated, shinks when cooled. Still, I would expect that these seals should handle extended periods at room temperature?
The only other thing I can think of could be an very active secoundary fermentation?
