I suppose you could damage something by overfill but I doubt you did. My guess is as the fluid expands with heat it could cause to much pressure and cause a hose or something to pop off or leak. As far as draining you can use a large turkey baster to suck some out. Be sure and use a new one and thow it out when your done. The contamination thing. If you want to drain it you could probably take the fitting off where it goes into or returns from the steering rack, but I don't know if that's a good idea, as one of the sides at least would be under pressure.

I'm not sure what would case the fluid to be low other than a leak unless it was low from the initial fill, or the people who put the new clamp on didn't top off properly after they fitted the new clamp.

I would use only MB power steering oil part# A 000 989 88 03 16