It has been leaking for a few weeks, I finally tracked down where it's coming from, see pics... the seat belt trim at the roof is sopping wet, and the water runs down each side of the roof liner as well. But a piece of cardboard there during the last rain shows that the water is dripping right down from that seat belt trim. Is it one of the two seals shown in a photo here, like the wiper wires or the brake wire?
Or maybe it's this, see antenna pic... I just noticed that one side of the seal is lifted a bit (left rear in picture) but the headliner underneath it down to that seat belt thing doesn't seem wet.
Any leaves or garbage caught in the rear door jamb area? If that can't drain out, water will find a way through the wiring grommet for the stop lamp.
Thanks for the responses. It was the antenna seal. I ordered a shark fin from the PriusChat store which will be here in two weeks, it goes over the existing so it'll be an all new seal. In meantime, I used a bit of marine calking to keep the water out until I mount the new antenna. Thanks again all.
I know nothing specific about the part. It's the store. Lots of fulfillment issues. My own personal experience was okay- I bought some accessories and got my stuff just fine, but these pages are full of stories of less positive moments.
Thanks for the input. The marine caulking seems to be working and should last awhile, hopefully the part arrives before too long.