I went to a recruiter today for an interview. He wants to send me to a company that I had an interview with six months ago; of course, I didn't remember that until I reached home and gone to file this interview along with the others. Should I tell him about this interview or should I stay hush mouth?
Unless you did something terrible on the interviewers desk I'd just tell the recruiter and not worry about it. 6 months is a long time in recruitment, and even if it's for the same hiring manager, the reasons that meant you didn't get it last time may no longer be relevant.
There could be a conflict on agencies, but in my experience few have global exclusives these days (only tends to be on an individual role), so be open and honest and you'll be OK.