Mag 12 Safe for submersible return pump?

[tranvictor]

I was just plumbing up my new tank, and I noticed that the Mag 12 (bought used) has some rust where the screws are. I was planning to use this pump as a submersible return, my sump isnt drilled. Has anybody used as a mag 12 as a submersible? Was there any adverse effect from the rust? Any help would be great.