Dishwasher Air gap
First, if the air gap leaks when the dishwasher is not on, then the drain might be partially clogged. If so, then the air gap is "working" correctly. The air gap is there to prevent clogs from backing up drain water from the sink or the dishwasher back into the dishwasher. The gap raises the dishwasher drain line above the level of the sink so the stopped-up water will level out in the dishashwer drain tube before heading back down into the dishwasher. The "air" opening of the air gap prevents a siphon from forming in the drain tube, which would allow the backed-up water from making it over that gravitational "hump."
If it is leaking while the dishwasher is on, then the drain plugs at the air gap might be reversed such that the dishwasher drain is "forcing" water up out of the air-gap.