I Had A Same Type of problem. Turned out it was some predrilled holes for the windshield. I had To Pull the Center ceiling liner to find while water Running or a Good rain. It looked like a predrilled hole that was not used. I guess As The windshield rubber aged it lost the seal it may had when...
Want to buy a Aft camper canvas door for 2006 SD 240, Just need the port side where the door is but will buy the whole aft if need be?
Thanks
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or sabotage142000@yahoo.com