You could wait and see if the fluid level drops more, but I'd for go for the compression test & oil analysis instead.

The reason I ask about the windshield is because of the heater core. It is possible to have a tiny leak there with the vapor escaping, but not dropping out. That too could be the cause of a leak. But the tell-tale sign of that would be a greasy windscreen on the inside. The water just evaporates, but the glycol sticks to the glass.