Leaking Mustang

Yeah, I just found out my 87 mustang is leaking onto the drivers side floorboard .. The car has been parked for a couple years so I dont mess with it everyday and that is why I had not noticed it sooner, the question I have is this. I notice the water comes down under the dash right in the left corner..Does it sound like a windshield leak.... or like a rust hole somewhere?..I know that is really vague for a description, but I dont know if it is common for these mustangs to leak at a certain point.. The other thing, the protective coating they put down under the carpet on the floor pans has cracked and flaked off due to the water, Is there anyway to repair the coating? Thanks for any help.......