Have had the same problem twice on my 04 Monterey and solved it both times.
I've heard the pressue test with bubble bath works pretty good, but I have no direct experience.
First solution: Unroll the slide topper. Use wood blocks with clamps or pins or some method to keep it from rolling up. The danger here is that if something slips when your hand is in the way you can loose your hand. After you're sure the awning/topper won't roll up, remove it an lay it on the roof. Now you should have access to the seams that go full length along the inner and out edge. Clean them and re-caulk. Not sure what is best, but I use acetone to clean and silicone to caulk. You should be able to reach the inside seam by lifting the wipe seal up a couple inches at a time.
If you can't get to the inside seam, I've seen it reached from the inside the coach. Bring the slide in about a foot, reach over the top. You need a helper if you do it this way. You have to put tubing over the caulk tube as an extension. The helper squeezes the lever on the caulk gun. Don't get caulk on your wife's pillow. If you do, switch it to your side of the bed.
Second solution: A tech replaced the spring in the topper/awning. When he put things back together the awning roll-up tube contacted the side of the coach before the slide was all the way in. It created a pressure that opened the slide about 1/16th of an inch and the rain came in while the slide was closed. I shimmed the mounting bracket and all was well.
Third solution: Your slide seals are damaged or deteriorating from age. I've not done this job and suspect it is difficult.
Fourth solution: The slide is out of adjustment and the seals are not compressing properly. I have not adjusted slides by myself, but have observed it. It looks a little tricky.
Good luck. I hate slide out leaks.