Have you tried measuring the 5v without any other boards being connected (which could be loading it down.) Do you have a voltage on the input side of the LM323?
I have seen a few tantalums go short before but this would probably blow the fuse. Pinrepair.com mentions that the tracks leading/from to BR2 can easily be broken so you could check the continunity of these. I also had a regulator go faulty a few nights ago where I could put a small load (100mA) across it it would measure fine but if I put a 2A load across it it just shut down. Hope these give you a few ideas.
regards Derek
