I don't doubt that the pano windows were originally built quite leak-proof. I've experienced rain leaks over the front windows twice and had to dig out caulk on the rail for the rockguards over the front windows. Do a thorough job removing the old caulk and then reseal with Sikaflex or Vulkem. Mask with tape to control the mess and then press and smear it in as well as you can. I haven't had to remove the rockguard rail yet and have succeeded with that.
I store under cover and still get this. The ultimate wisdom is, "They all leak."
says, "The price of freedom is eternal maintenance."