The gap between glass and pewter is sealed with putty (at least on my old one). Scrape the putty out carefully and replace it. If you can't do this, or if there is no putty, superglue works really well for small cracks etc. I have one which cracked at the handle and has been fine for over 5 years after supergluing. Make sure it's cvompletely dry though and do it inside and out.

Don't use lead or solder, both of which have a higher melting point than the high tin content alloy which the pewter is made of.

:-)