(Portland, OR)  --  A man is being treated for a serious stab wound he suffered during an argument behind a Southeast Portland gas station.  Police say officers found the victim at a Shell station on Stark Street around one p.m. yesterday.  Authorities say the suspect, who's still at large, is a homeless man who's described as white, in his 20s, five-feet-seven, with a slim build and short, brown hair.