That's a completely different system to my 2008 non-abs Tenere. It looks like the opening relies on sealing against the tank cap and venting through the small hole in it. I suspect you filler cap assembly is at fault and this hole is block or has not been drilled properly. This would explain why a new tank didn't cure the problem as they would almost certainly have used your old filler cap.

Try leaving it in the sun with the cap loose like I said. If it doesn't spill out, then I'd suggest a trip to the dealer and get a new filler cap assembly fitted under warranty.

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