Found this advertised on the web. Not tried it myself, but it looks like it should do the job
Oven Door and Cooker Seal Repair Kit
This is a specialised industrial RTV silicone adhesive and sealant which is flame retardant and non toxic designed for bonding the glass back into your oven / cooker door when the original adhesive fails
Bonds and seals glass, metals, silicone rubber and most rigid plastics.
http://www.intek-uk.com/ovenkit.htm
Liz, May 2005