Advise needed to track down ceiling leak

[GaDawgFan]

I have a discolored area on the ceiling in rear bedroom. I obviously have a leak but have no idea how to find it. The coach stays in a covered facility, so the only exposure to the elements is when we are on a trip. The discolored ceiling carpet is about 2 feet long and runs above the wall line above the window/emergency exit. I have visually inspected the roof gutter and have not spotted any obvious breaches. Any suggestions?

[Indy Itasca]

I would suspect the roof seal even if it looks good visually. The other suspect would be the back end cap where it joins the roof. Both need inspection every 6 months and re-caulking often. There are several threads here about roof caulk and almost endless debate about which product is the best.