Welcome. And on the contrary, you ARE in the right place. Now if you had a 1999 Opel Omega, we'd be a bit hard pressed to help you. Oh wait, that's a Cadillac Catera. But this site is devoted to the "classic" Opels, imported into North America between 1964 and 1975. And a few others that snuck in when nobody was watching...
As for your Manta' driver side window, I would suggest you try Charles Goin at Goin' Manta (
http://www.opelmanta.com/ ) or David Ponder at
http://www.opeljunkyard.com/ or John Grosh at
http://home.messiah.edu/~jgrosh/Blitz Parts.htm or Todd at Opels Unlimited (
http://www.opelsunl.com/). Or just ask on this forum (I moved your thread to the "Manta" forum) and perhaps one of the members will have a spare window.
By the way, I deleted your duplicate post in the "windows" forum. We have enough posts here without having two of each.
HTH