I am looking at the same problem with some corrosion small holes in my front turn signals that were stripped and media tumbled. I have just ordered and received some muggy weld to see if I can add some metal to the thin and perforated pot metal housing. It looks good on video (no affiliation)...
http://muggyweld.com/pot-metal-repair
I'll try to take some before and after pictures. The nice thing is that the metal that you add can be sanded and smoothed afterwards.
Tonger