G'Day Matt, I got caught in the 'leaking pet bottles affair' this was quite a while ago. What I found was; there are/were 2 styles of brown pets' on the market, one had 4 indents on the base and one style had 5. I found that all the bottles with 4 indents would leak from the same point when they got up to pressure. To cut a long story short I had the supplier replace 10 cartons of faulty (leaking) bottles with the later design and never had another problem. After that I 'saw the light' and moved over to kegs :-} I have given most of my brown 750ml pets away, now I use the 1125ml Coles pets for take outs and never had a problem, you have to store them in the dark!. Check before you buy I wouldn't touch the brown pets with 4 indents it was a design/manufacturing flaw.
Cheers