The base has molded terminal locations numbered 1-4, two of which are
empty:

http://i36.tinypic.com/e6x542.jpg

Markings on the side a

B41111-B7108-T
1000uF 40V-
GERMANY
GPF DIN 41332 06.78

I find a few references to a Siemens part that is similar:

http://www.screenghost.com/shop/show.asp?ID=74#

but no datasheet can I find. Can someone more resourceful than I find one?

I cut open one of these caps. It is paper & foil (or so it seems) spiral
wrap
construction. Can polarity be determined by internal construction? Is the
center terminal always one pole (ie, always +)?

Thanks.

AFAIK Germans always write a ONE with a tag ( opposite 2) and a 7 with a tag
through it that makes it look like a lower case t.
So I suggest the - really is MINUS.