Your gonna get a lot of opinions..
I tried Kool Seal, looked nice, lasted less than one yr and started to crack and look thin in places.. by yr two, it was pretty much worn off..
Yes, I cleaned, scrubbed, prepped and no it didn't last.
In my case, I applied over a worn fiberglass roof, applied several coats.
I will be very frank and honest about these liquid fixes in a can.. They are very temporary at best, and will require reapplication often.. They are as thin as paint, you simply cannot replace the thickness of the original roofing material..
If your roof has no rips, tears, cracks and it just doesn't look "pretty white" anymore, DON'T DO IT! Don't go there with liquid in the can fixes, you are just wasting your money and time.
Your roof DOES NOT "have to be blinding white" to still function and absolutely nothing you can slather on it from a can is going to preserve it or give longer life.
If your roof has some rips, tears, cracks, DON'T DO IT! The liquid fixes in a can will not have enough body to bridge and repair those issues and will fail.
In my case and NEW roof over top of the old fiberglass was the only real fix because of cracks in the fiberglass that just defied staying repaired and the high cost of automotive grade paints being out of this world in cost.