Can anyone tell me what causes this and how to fix it ??

 

I assume it's from repeated condensation where the excess water pools up in the pipe.
And eventually causes rusting.
Mother's metal polish should get that right off.

 

ok got it thanks !!

 

My guess is you don't keep your G parked in a garage so it spends it's life outside in the elements of your wonderful right coast weather. You probably have rust in other areas you haven't discovered yet. Clean those tips then give em a shot of WD40 to slow the rust down.
Gary

 

WD40 and steel wool will take it right off just make sure when you wash you car you apply another coat of WD40 to the tips this should help you out