Hate to see it!! One thing to keep in mind, no company that sells Tonneaus is going to guarantee no leaks.
With the right amount of time, patience, and sealant you can get it there. I have the MX4 (Bak version of yours) and it took time and tinkering to get it to where I have 99% coverage.
4 tips:
get rid of the weather stripping they give. It sucks. Find something thinner and wider for the front.
chop down / cut the drain tubes up front for the rails. This helps and allow proper drainage for leak into the rails.
wait until it’s sunny, crawl in the back with the cover on and close the gate. Look for light. If it’s at the rear, loosen up front and adjust the cover, If it’s not on a functioning joint - put some silicone on it
make sure the “flaps” on the side are flat and straight. I had bad leaks from the side and noticed that the flaps were getting folded under. I rarely fully unfold the cover so just checking this when I close it again is easy enough.
there is a ton of hate for the MX4 and it’s GM counterpart. To each their own. I’ve found it as great quality with great features (the full fold up
is a lifesaver), but it took me some TLC to make it that way.
good luck!!