Hi... I had much the same situation on my vintage '88 Honey.
I finally this year tackled it because we sprung a leak. I ended up buying a multitool (kind of like a vibrating scraper) and hired my son to climb up there and scrape all that gunk off... I didn't think it would come off, but the roof was aluminum underneath it with fiberglass sides, so it worked out ok... took him several days to get it finished to the point where it was clean enough to do something with. We then put eternabond on it. It got the leak. After the eternabond, we caulked with Dicor. Eventually I will paint snowcoat on it to help keep it cooler when we are boondocking in the summertime where there isn't any shade.
He had to sharpen the scraping blade a couple of times during the process because it would get dull pretty quickly.
Good luck. You may not need a new roof, but you certainly need to fix the leak and repair the damage it has caused underneath. Sometimes, the drain for the condensation gets plugged and the water must go somewhere... if it dips a little there, it could pool there and if the caulk or sealant was cracked it might have worked it's way inside.
Martha (AKA RVM45), Bob, and Bess the Border collie
22'Honey Sportscruiser on a 1988 Ford Econoline.
Sometimes towing a powered Parachute.