I had one of those leaks on my truck camper with the over the stove vent, it is SOOO frustrating. Of course when it is dry outside no leak, you get rain and it leaks, you repair it and by then the rain has stopped and of course the leak stopped, starts raining and the leak starts. If I had a garage to take it into during the rain to work on it it would have been better but I didn't.
The WOW moment was during a bad rain storm and it started to leak, I was able to track the little stream of water to the vent so I took the fan and light off inside and started to poke around with a flash light like I had done so many times before. This time I saw the water coming in and running along the side of the cut so I cleaned the cut with a rag and bingo there was a little drill hole that they put in when building it that the water was traveling through. Fixed it, dried everything up and no more leak.
I hope your idea works as sometimes there is no obvious problem/fix so you just have to work on possible solutions.
