I too purchased a garden window in 1997. The bottom of it is separating.Home Depot said that the window has a lifetime warranty on it and gave me a number to call. The window makers asked me if there was a bracket put under the window I said no that Home depot said you don't use a bracket. The contractor who installs windows for a living also said that it did not call for brackets. This window maker said that they would pay 50% of the cost of a new window on a lifetime warranty. In 97 no brackets were called for. Now they say they won't warrant the whole window because no brackets were used. The whole thing is a crooked scam. The truth is that the glue used in the laminated plywood because of condensation has given away, allowing the plywood to separate.
Window brackets would not prevent this from happening.