I just checked mine and it doesn't seem to have a drip pan. From your pic it looks like a major project to change it out. I had to also replace half a dozen screws due to the heads rusting off from the molding leaks. My leak is now coming from the top of that slide channel and once it drips down it goes past the inner rubber seals into the coach. I've poured water all over the area from the bottom to the top of the slide and can't get it to leak. When it rains it leaks.
Maybe it's coming in from the top and takes awhile to get down to the bottom?
Good thing I'm retired and have the time to work on it.
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