2009 XC70 with mysterious leak

Hey all, just bought my first Volvo wagon after many years of admiration. It's getting old, but I'm hopeful it has some good years still ahead of it. The car has 200k km (125k miles) and in many ways seems to be in great shape. It had a few issues that I knew about when I purchased it, and I'm working my way through them (bad wheel bearing, front flex pipe leak). One issue I didn't know about is that the car seems to have a leak.

We had a crazy rain storm that started the day I bought the car and lasted a couple of days. The next morning the headliner was wet near the windshield and the cabin light assembly had water dripping out of it. And, since then, it sounds like there is about a quart of water under the dash (or under the carpets way up front?) that sloshes back and forth when I go around corners.

My first thought was that it could be the sunroof drains, but I've poured water down them and the seem fine. I sent a blast of air from my compressor down for good measure. I suppose the rain could have overwhelmed the diameter of the tubes?

My second thought is a windshield leak, but the windshield itself has not been wet on the inside, and after another big rain last night there is water in the cabin light again but the headliner feels dry.

My third thought is that the water in dash (or floor) and the water in the headliner might be unrelated... and maybe I have an AC drain clog? I'm going to try hitting that with compressor later today.

I'm not in a great position time-wise or money-wise to chase this issue around the car forever. I'd love any advice from the group about this, including whether people feel it's worth trying some kind of sealant at the top of the windscreen (I'm hoping to avoid having to get it pulled and risking it getting broken in the process).

Thank you in advance! Like I said, I've always wanted one of these, and I'm hoping to slowly convert it to a low-intensity overlander/camping base camp over the next couple of years... provided it doesn't turn out to be riddled with these kids of small issues.

Cheers.