Our boat is 30 yrs old and I have discoloured/chalky navy blue geloat on my topsides (although the white gel is fine). I have tried using cutting paste with and without a car polisher but to no effect. I have also tried rubbing a small patch continuously for 40 mins with paste to see if elbow grease alone was the key. Still no effect. I presume the discolouration is some form of oxidisation. Perhaps some chemical treatments are available? ( There is discussion on the noticeboard of professional valet type services. What do they use? Is commercially it available?). Any experience or useful tips gratefully received before I admit defeat and paint it.