I started brewing less than a year ago. In that time I've acquired about 60 swing top bottles, and filled about 200, I estimate I've filled each bottle less than 5 times. The last batches I made were a biere de Garde, an ESB and a Xmas ale. Unfortunately the carbonation of the biere de Garde was totally lacking, essentially on a par with the bitter, which I put down to some kind of mistake (not enough sugar, not enough time at room temp) until I started cracking open the crown cap bottles. One of them was a gusher and the others had big foamy euro style heads. I now believe the swing tops are to blame and were not holding pressure.
My question therefore is:
How long should swing tops be viable for?
And also: Is there anything I can do to improve their performance short of replacing all the seals? Is there anything I've done that could be to blame for them having deteriorated? I usually just rinse bottles immediately after use then fill with milton/VWP for 15 mins and rinse immediately before filling, and leave the tops in a bowl of the same.