Stain aroung Fuel fill

[NormH]

I have a 2006 2520XLD which seems to build a yellow brown stain around the fuel fill. This wasn't apparent the first year I had boat, but now it appears after a couple of fills. The stain runs 4-5 inches towards the rear of the boat. I have been able to clean it up with Barkeepers, but it seems to be waring the finish down some. Does anyone know if this is from gas fumes or rust coming up from the mounting? Would it help to re-caulk the fitting, any help would be appreciate.
Thanks Norm

 

[Megabyte]

Could the stain be caused by StaBil during the fueling process?
StaBil will make that kind of stain when it contacts the gelcoat.

I clean mine with liquid bleach. :wink:

 

[DaleH]

If running ethanol or E10 fuels ... it stains the hull more than MTBE-based fuels ...

 

[NormH]

I have been using the Yamaha Ring Free every time I fuel as recommended by Yamaha. This and Dale's idea about the e10, I beleive all the gas in Calif has this added now. Like the bleach idea I'll give this a try next time thanks for the help.
Norm