The torrent is easily found searching for Possession 1981. I'm not usually a torrent movie person, but, well, when there's no other reasonable way... Also, if you're really lacking in self respect, it's on YouTube.^i wanna see that so bad. i found it after IMDBing the dime from The Tenant. it's not in region 1 print though.
^I've always found 80's horror movie gore to be more realistic than present day horror movie gore. Probably because back then they didn't have CGI and had to make due with make up and props alone. Old school special effects is a dying art unfortunately.