There is another WED-15 Treadwell on the Sandcrawler, though, which wasn't in the sale. WED-15-I662
Side note. To be honest, while some (read: wookieepedia) treat the Septoid
(spidery droid) as basically a Treadwell with a lot of extra arms, I've always felt it was a different model entirely, albeit by the same manufacturer.
It doesn't have the same head. It doesn't have the same base (more enclosed). The only real similarity is that it has a similar layout: a flat base with treads and an aerial, and a stick body. But even the body differs from Treadwell's; it's more uniform and the mount is raised off the base and surrounded by a ring type of mount for the arms.
Edit edit: Bah, ignore this edit. The forum was eating the Septoid link above. Now it is working fine. No idea what's up with that, though I still can't link insert the images from the gallery inline.