Any information on where the oil leak was and how it was fixed?

If the bike runs good, shifts smooth, and rides good, I wouldn't worry too much about the previous oil leaks, depending on where it was leaking from. Unless there was damage to the engine cases from previous drops, the leaks where probably caused by leaky gaskets, which, for the most part, are an easy fix.

If I were you or your friend, I'd try to talk the seller down a bit more before committing to buy. $3000 for a banged up '04 is a fair price.