Send it back. The only caveat being that if the lens was a smoking good price, and you don't mind taking a few minutes to clean it yourself. It could be separation, but it doesn't look like it to me, even though the Mamiya TLR lenses for some reason are very prone to separation.
Looking at it closer, you can see the retaining ring has been removed (or an attempt to remove it) in the past. I'd send it back.
@jordanstarr - the haze I usually see almost looks like the glass was sprayed with an ultra-fine mist of moisture, so I usually see some amount of 'spotting'. But, it could be anything without seeing it in person.