Well, I agree about the difference between circling the drain and climbing out of a hole. The defining piece of information for me is the $500 need to cover a delay in a transfer. A hole climber would have paid that back immediately after the delay was resolved. A drain-circler would have kept the money and made another excuse. The brother is a drain-circler.
+1. There is more than enough information here that the recent past is a bunch of empty promises intended to convince his siblings that he has turned over a new leaf and deserves more gifts (it's only a loan if it's ever paid back) .
But I guarantee you that youngest brother and I are sticking to our bottom lines! So, the next time City brother comes around with a request for even a little more money (which, honestly, we are expecting will happen), we are following the advice of Tightwad, catchingup, and DoingHomework and telling him “no”! Each of you are probably right that it is time for him to learn to fend for himself, but I’m not ready to tell him that today because he has literally just arrived in City, after a 5000 mile drive, to seek his dream career. However, certainly after this second loan, I will not hesitate.
Good luck. Knowing that you are being manipulated is the first step along the path of resisting that manipulation.
Do come back when (not if) he asks for more and tell us what happens!