Is this prefilter i hear of some sort of sock device that mounts between the tank and the cap ring? Like a screen or sorts? Does that hamper fueling at all?
I also wouldn't be surprised if this isn't the same universal in-tank fuel pump that most bikes have. Seen the same exact part in a Husqvarna, Aprilia and Triumph. Although in all those cases, never saw any serious gunk of sorts, even with higher millage or race fuel used. You would think that a bike that's used only 1000 miles a year would have all sorts of gunk around the pump and filter.
I'm gonna guess there's some sort of production sealant used that's getting in with the fuel. I think a universal inline filter is not a bad option either; considering the sensitivity of the fuel injectors.
Aprilia Supermotos had issues with them, mainly from drying out while sitting or running the fuel low. But in that case, they would seeze up; requireing a few bangs with a hammer to fix :-)