My HD breather kit had a small hairline crack in the weld on the crossover tube. Caused the same thing you mentioned in your post except mine was on the rear banjo bolt. A friend at the dealer said he had seen that before so he ordered a new crossover for me. No prob's since. My scoot also gets around the 40's for mileage. But I like to leave the corners and the lights pretty good so I don't doubt it a bit... Good luck with the leak.