There is a valid reason for things like headlights, brake lights, and turn signals to not be sealed air tight, and it has to do with the large difference in working temperatures those parts experience due to the heat of the bulbs. There is no such requirement for gauges, but Harley's gauges have never been sealed as far back as I can remember. You have to realize that Harley probably pays less than ten bucks for the complete set of gauges, and you don't get sealed gauges for what they pay. They've gotten away with blowing people off over this common customer complaint for decades, people keep accepting the BS and keep buying the product so obviously it's not a problem.
Jerry