I have never heard of this absolutely rare name, but it seems to exist in Germany,both as a forename and a surname.
WIN could be
German or English = friend
BOR could go back to Slavonic borti = fight (borg seems unlikely, as most hits point towards the east, Poland etc.)
http://www.vorname.com/name,Borwin.html
(Unfortunately my digital version of Seibickes HDV starts with the letter F.)