It started as a slow leak, but it isn't slow anymore (we're not driving it, but I started it up recently just to move it and lost about a quart of coolant in a few minutes of idling).
My theory is that because of the plastic shield under the engine, the leaks land on the shield and blow off while driving, and unless you sit in one place for an extended period idling, there won't be enough on the tray to leak to the ground until the problem gets bad (there are lateral stiffening ridges on the tray that allow it to hold several ounces of liquid, but bouncing down the road and wind will remove it while driving).
Initially, we were seeing small puddles on the ground under the car. We wouldn't have noticed it if the undertray/splash shield were still in place under the engine. But the dealer had removed it looking for a clacking noise, and then never put it back on. (And I didn't notice that the shield was gone for several months, by which time the dealer denied that it was their doing. They also cracked the plastic cowl piece, likely from closing the hood with something on the cowl. Those two things were why I stopped going to the dealer for service, and not going to the dealer for service (for the past year) is one of the reasons that Mazda gave for not covering the repair costs).
