you can buy a panel for lower part of door then replace if you are confident at diy or you could phone a double glazing repair company or glazier in your area and thy can do this for you,it would save a lot of money rather than buying a new door.If you are doing it yourself you can buy a panel from north east panels phone 0191 4153111 or hurst plastics phone 01482 790790.hope this helps
shaun www.sdwupvcrepair.co.uk
July 2008