JunkBeast wanders from the 1st large scrapyard to the left of the zone-in (which is past the factory), and from there, left down the path towards Xanamech's room. I've seen him 5 times total, each time in differant places between the two points. He usually ends up pathing around a room, but I have seen him on the path once.
Curiously, the busted power carrier also roams that particular path, or one similar to it. Could they be related? I've killed the BPC a few dozen times trying to prove a link, but so far no success. Haven't been able to put a really good block of time into it, just stabbed at killing the BPC once or twice every few days.