Might have exaggerated the largeness of it, but it was big enough to pool in the corner of the trunk under the light/antenna. But I've already soaked up the water with some towels.
For now, until I can replace the gasket, I closed a small tarp in the corner of the trunk to cover the light and antenna (in case it's leaking through there too). Probably gonna replace both sides at the same time since my car is now 20 years old....