The pressure wouldn't drop if there was a leak as the set pressure is the set pressure meaning less would be going into the keg if there was a leak.
You don't know how long after originally setting the pressure it dropped as you noticed the next day. It could well have happened quickly meaning the system settling down.
Has it dropped again or gone up? If not I wouldn't worry, just check soon after when you do your next keg.
Besides stirring I get good aeration/foam by letting the tap water hit the handle of the stirring spoon allow the water to spray down into the fermenter. The spoon is sat on the fermenter handle/grip moulding inside and angled up to rest on the fermenter lip.
Aerate before adding the yeast, give a good stir then sprinkle the yeast on top of the foam. Never failed in don't know how many brews. I found if you add the yeast and then aerate by stirring, half the yeast is stuck to the side of the fermenter above the foam.