Rolex air king

[jubilee5500]

Hi guys I am new to this site, and need some help info I have a rolex air king 5500 registered design 1737541 I think it dates back to 1968. my question is that I have noticed on the gold dials some pitting is this normal? was it a flaw with the gold dial? I took it to a good watch repairer who used to work for rolex and he suggested that moisture might be getting in and he might need to replace the screw where the crown goes in and pressure test it? I don't wear it in the water should there also be a waterproof seal inside?
I'm in Sydney Australia and not sure on how much a proper rolex service would cost or is it worth it thanks guys