If you complain to Pepsi (1 800 433 2652) and say you bought a 4 PK of Amp and say that one of them were leaking or something, they will send you a coupon.
I found the .doc sheet that already has a very clear copy of the coupon on it. All you have to do is print the coupon out, cut it clearly and take it to a store and use it. The barcode is the same on all the coupons, so you are fine that way too.
Here is a picture of the coupon. It looks way clearer in the .doc file.