The fluid is transferring from the trans to the primary, so for a vent in the primary to supposedly fix it that means they think the primary is somehow developing a partial vacuum. The trans is already vented to atmosphere, so it can't be a buildup of pressure in the trans unless they somehow managed to screw up the trans venting system during the redesign of the trans case. So my next question is, how does the primary develop a vacuum? This is another issue like the sumping issue, where Harley either has no clue or they do know what's wrong but are looking for a cheap band-aid instead of fixing the root cause. The older transmissions, 5 speed and 6 speed Cruise Drive, didn't have this problem. The problem seems to have started in 2014 as best I can tell, after Harley made changes to the Cruise Drive trans, and got worse when they went to the oil cooled M8's for 2017. Replacing a shaft spacer and seal fixes many of the 2014-2016 bikes, but not the 2017-2018 bikes. Hmmmmm.
Jerry