Get a tube of sealant and seal up that top seam. I’d recommend Geocel Pro Flex. I usually buy the clear but it looks like it’s sold out right now by Amazon. It should be around $10 a tube. Clean up the seam and caulk anything that looks like there should be caulk or water could get in. That vertical seal is open on ours as well. The way I looked at it is water can run in the top but will just run out the bottom as long as the seams around it are sealed.