I purchased a 12 pack of swing-top bottles at a decent price. I only now noticed that over time as I drank through the batch, the bottles were less and less carbonated, ranging from perfect carbonation in the early bottles to virtually no carbonation in the later bottles. I've never had an issue with losing carbonation in previous batches in capped bottles, so I can rule out my technique for carbonating. In hindsight I'm starting to think the bottles were a great price because, well, they're cheap bottles.
I'd like to avoid buying a more expensive set of bottles (and risking the same results). Is there anything I can do to strengthen the seal of the gaskets or upgrade the seals with a better option for my next batch?