Hi all,
I thought I might add my 2 cents to this conversation. It is important to finish off with a very fine file and then polish out the area. Any file marks may cause cracks to return. Another point - make sure you get all of the crack. Where the crack ends can sometimes be almost invisible and if you do not get it all it will return! This maybe overkill but you can use dye penetrant to find where it ends.
Mike Short,
Austin TX.