I don't know what your top is made of but I have an antique Corvette that had a new White top put on it in 1974. I believe its vinyl. with vinyl stitching. Rot proof.

1. NEVER store the car with the top down.

2. Always cover top when not in use " I use an old sheet under car cover.

3. Your not gonna believe this but at least once a year I scrub the top with a stiff brush and "Comet" cleanser yes I said Comet
the top is 29 years old and look as good as the day it was installed. I have never used anything on plastic window just a damp cloth and its crystal clear.

PS
I love the car you just got if it runs as good as it looks you got a winner