Upload & Sell: On
Before touching it, I would first use the heck out of the thing for a few days, just to prove to myself that everything is functioning properly: AF, MF, zoom, aperture blades, etc... If anything is functionally broken, I would return it.
Then, inspect all of the images you have closely. Is there anything you see that suggests the spots have any noticeable impact on IQ? If not, then use the lens as-is until either you see something that's objectionable, or the spots finally drive you insane.
Then, and only then, would I go so far as disassembly and cleaning. Remember, if you're not a pro at this, you must go in assuming the worst, that you could screw it up and end with a paper weight. I wouldn't risk that unless there was a clear benefit, or else the $300 steal turns into a sink-hole.
So, take some shots and post them ASAP