I have more than 20 and have had to have 3 of those replaced throughout the years. I had zero troubles with getting them replaced just send it in and they send you a new one. 2 of them I thought they would fix but they sent me a new one instead. I only had one break that was not my fault when I was reeling in a fish but I was horsing a 25 lb cobia pretty good. But it most likely had a crack in the carbon prior to that. I did a rapid replacemnt on 1 of them which cost me $50.00 bucks so that I would get it without sending mine in first and the other 2 I sent in and they replaced within 2 weeks including ship time. All my rods are IMX or GLX but I would imagine they offer the same replacements for GL2 as well. 1 of them was replaced prior to Shimanno owning and the other 2 was after and did not seem to make a difference, warranty replacement was still good.
I highly recomend them they are great rods.
I will also add I never had to show proof or purchase or a reciept.