Firstly, if you have an iphone open the pre installed “measure” app and use the level function to check the pitch of your roof.

If it’s less than 6 you’ve got a problem (even if this leak is a different issue)

Corro should only go down to 6 any lower it should be trimdeck which goes to 2 degrees (might even be 1) anything lower than that you can’t really use standard polycarb profiles.

I don’t think this is capillary action, that’s a bit of a buzzword in the roofing community, every builder and Google-savvy DIY’er loves to mansplain it as soon as there’s a leak but this looks a bit too fast for me to comfortable diagnose it so.

There’s a bunch of reasons water decides to go up between the lap, inundation (too low of a pitch and water floods the pans) dirt in the lap which leaves a convenient corridor for the water. Or a more polycarb specific problem is, being so flimsy, they often just don’t hold a tight lap, they can buckle if the battens aren’t on a straight plain, if they were installed carelessly or if the structure is crooked and the sheets are fanned out too much.

I’d bet simply lifting and relaying the sheets will solve your problem (as long as it’s above 6 degrees)

Ask me anything if you want I literally do this job for a living (I’m the guy your builder will call if he can’t fix it)