Hi David,
I primarily only collect Badges/medasl and have a nice group of Schwerin U-Boot badges.
I did see one cased Uboot sextant sell sometime in the last couple of years for +- $1200 I believe.
You can post pics on the WAF forum I belong to:
http://www.wehrmacht-awards.com/forums/index.php
and the Kriegs guys can sure help you out with authenticy and maybe value. If not you can email me pics & I'll be happy to post them for you.
affjm96@wavecable.com
Greg