My roof is 20 years old. I applied a gallon of Kool Seal that a friend gave me because he bought a new MH and it looked good for about 6 years. It is wearing away and I can start to see the original EPDM roof underneath. In contrast my friend has the same year roof but never coated it and his roof is completely black because all the white outer surface has worn off. Neither roofs leak as long as you check and recaulk or use the Eternabond tape. I just think a white roof keeps the MH cooler in the summer. I would coat it now if the outer layer of rubber has started to slough off.