I just went through this and attempted to repair myself. Not an easy job and overall it turned out OK although I'll have to repaint an area over but that will be next years job, got bigger fish to fry now.
Here is a post I did
Followed by this after I had some epoxy get on the side of the caoch.
I ended up redoing a section I had quickly fixed last year along with the epoxy area. Not perfect but good enough for now.
The way Monaco constructed the coach is is almost impossible to repair. The sides are mated to the walls, walls then mounted to the chassis, and then the top and rear cap is installed along with the lower fiberglass. The top, cap, and bottom fiberglass overlap the side, no way to get to the problem. The beltline moldling covers the seam.
My leak looks like it was from the top beltline towards the back, water entered and then migrated down.
I removed all the old caulk from the beltine all the way around and then used Geocel.