Thanks for the reply 🙂 I took it in for an inspection and the mechanic said it's OK for the age actually. I plan to take off some of the rust with a wirebrush drill attachement then treat it. Various perople have suggested different methods for treating it, the only thing in common so far is that they involve a lot of mess! But that's fine by me. I will probably use waxoyl like you say as I have some experience with it and I just want to stop it getting worse.