Ballerbbay: These are all good questions, and I am pretty sure that we won't know the answers for quite some time. But part of the fun is quessing and theorizing in the meantime. I also think RAB would need some help, and as somebody mentioned in this forum, I think a houselef would be pretty good help in this situation, who else could be persuaded to make that trip. I don't think it was Sirius, I think Sirius would have told Dumbledore about it a long time ago, and between prison, being on the run, being locked in, and dying, I don't think he had the time.