Dear Harry,
I too, like you, decided to clean my Neff oven, took the door off, and the inner glass fell out. After a bit of research (including the fact that it would cost me £700 to get a new cooker) I found a product via a company called AB Sealants Ltd in Andover Hants. Tel: 01264 359984 E-mail: sales@absealants.co.uk. I thought it would do the job but rang first to check and ask a few questions. I was answered on the second ring, spoke to a very helpful gent. who told me I was ordering the correct item (and that if I already had a mastic gun, then I wouldn't need to order one) so I ordered a sealant called 'SILIRUB HTo -A' (have a look at the website) and a mastic gun to go with it. It arrived by post the next morning and I used it that day. He advised leaving it at least overnight if possible, but as I wanted to be ultra cautious, I left it 36 hours! All I can say is - it's brilliant! Just make sure you have cleaned all the old gunk off first. The seal is perfect, the door is back on the cooker and it all works perfectly. The total cost (incl. P&P, mastic gun, VAT and the sealant) was the princely sum of £12.25. All I can do is highly recommend it, and the company. Good luck!
Sue, January 2008