Andy
If it's cracked at the top, is it across it or around the edge? Either from your description it sounds like one of two thongs, either it got dented in the past and was filled then over the years the filler has shrunk back slightly and caused the cracking or it has rusted and has caused the cracking or a combo of both. If the crack does not extend to where the wing meets the body you might be able to get away with a repair. If it's filler only the it's a matter only of rubbing back to bare metal, re-applying, preparing and finishing with primer and paint. If it is rust then if not excessive it might be repairable on situe by cutting out and having a plate mig welded in, and then finishing. If you have the paint code you should be able to get the colour, bear in mind that you need to be prepared for slight change on match due to years of sun on it. If pockets are shallow, then have a look at YouTube at how to do this type of repair for filling and paint prep, if you take your time and don't rush it is possible to do yourself, rubbing down, prep and painting, the key is careful and meticulous prep. The secret with spraying paint is right temperature and build up coats a little at a time. Then at the end very light rubbing back with 1800 grit wet and dry in soapy water, then use a medium cutting polish and then a final polish. You should leave paint at last 24 hours to harden before cutting and polishing. I would expect your car to be painted with cellulose paint from original, unless it has been resprayed.
If you need it plating then a local chap should be able to mig in a shaped plate for a reasonable fee.
I have done similar stuff in the past and it is possible to get very good results.
