FYI:

While a leaking gear cylinder may be a possible cause, it's not always the case, if you see that once pressure goes down, the valve seems to work, it's blow-by, you have to check both valve and gear cylinders. You can use BVM o-ring lube or RC car diff silicon oil to seal the gear cylinder o-rings: DO NOT use petroleum based lubricants to do this, you'll ruin the o-rings

The exhaust port you point out will also put out air from a cylinder(s) (gear or door) when operating, the adjustment screws control the rate of air flow out, that's how the valve delays action, once there is no pressure on the "open" side of a cylinder, the plunger inside the valve moves to execute the next sequence. The valve uses the principle of pressure differential(inside the valve and on the gear or door cylinders) to sequence the moves.