I had a 2003 Legend 356 with the same problem. I decided that the gel coat crazing and the discolouration were not connected. I had the gel coat repaired, it didn't cost much and the brown stain cleaned off easily, possibly contamination from the inside of the tube.
fixings are screwed to glassed-in aluminium plates, take care with these as I had to drill out some screws on hinges.
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