repl belt its for sure bad now. belt dressing will make things worse on serp belts. it could be a number of other issues, like water pump,idler or alt bearing but start with new belt and ck all belt driven parts while belt is off
I also don't believe 'dressing' makes the belts taste any better. I would also recommend replacing the belt , and also clean as much of that stuff off the pulleys. Brake cleaner probably would work , maybe suggestion of something better to clean it with from someone else?
YOU PUT BELT DRESSING ON YOUR SERPENTINE BELT? HOW MANY CANS? DID YOU SPRAY BELT DRESSING IN THE PULLEY? MAYBE YOU PUT TOO MUCH BELT DRESSING. MAYBE YOU NEED A NEW BELT. GET A NEW BELT AND PUT IT ON AFTER YOU CLEAN UP ALL YOUR BELT DRESSING ON YOUR PULLEYS. PUT NO BELT DRESSING ON THIS TIME.