Okay so you need a unit made good again.
Go to a glass supplier get them to take it out and temporary glaze it, then the time to strip it apart and then use the existing glass that may be scratched after 20 years or so badly failed that you cannot get the staining out. Then another visit to reglaze. Now compare to measure the unit, get a new one made and refit.
I think you will find option 2 cheaper and quicker. We strip units apart that need replacing but only if it has a lead feature or bevel cluster on it.
Go to a glass supplier get them to take it out and temporary glaze it, then the time to strip it apart and then use the existing glass that may be scratched after 20 years or so badly failed that you cannot get the staining out. Then another visit to reglaze. Now compare to measure the unit, get a new one made and refit.
I think you will find option 2 cheaper and quicker. We strip units apart that need replacing but only if it has a lead feature or bevel cluster on it.