Most recent model convertibles come with glass rear windows. Glass windows are an enormous improvement over plastic windows used in older tops because glass will not brown or scratch. A glass window should last the life of the top.
The problem with glass windows is that they break. Most breakage is due to vandalism. Vandals love to smash glass windows. However, a surprisingly large number of breakages result from "operator error". These are situations where normal top operation is impeded in some way. In a very common scenario, the window breaks because items stored in the boot prevent it from folding down properly.
Glass window tops come in two types: one-piece and two-piece. One-piece tops attach the glass into a single piece of top material. Two-piece tops utilize a separate rear window section to hold the glass. In both cases the glass window is permanently fused to the surrounding top material using a high-strength production process that cannot be duplicated outside the factory. Therefore, when glass breaks it cannot (except for two models) be replaced itself. One-piece tops require the entire top to be replaced. In two-piece tops the rear window section must be replaced.
Besides breakage, common glass window problems are glass separation from the surrounding top material, and the heater/defroster tabs falling off. Under certain conditions, glass can be glued back to the surrounding top material. Otherwise, part or all of the top will need to be replaced. Heater/defroster tabs can be glued back on the window using special conductive glue
If you're having a problem involving your rear convertible window, please visit us in Santa Clara so we can discuss your options. Also visit Convertible Top Care section of our Convertible Top and Interior Care Guide for information on cleaning glass rear windows.