I was frustrated with a 35 year old vinyl roof with a grain. Tried everything. What worked for me: 1. SOAK w/vinyl cleaner (Tutle Wax, Meguiers,etc) 2. Rub in cleaner with Mr. Clean Magic Sponge 3. Get into smallest pores with 0000 steel wool lightly 4. Rinse w/clean water and very little detergent.
I do not not know if you can see the difference in the pic but it is dramatic in person.