Warm water and heated white vinegar.
I have read in the past that people have used a car wax polish and buffed it up to restore the shine.
Have you tried just a damp microfiber cloth? Norwex is my favorite - especially the window cloth because it gets rid of ALL the streaks!! https://maurawhite.norwex.biz/en_US/customer/shop/product-detail/466103?categoryName=Cleaning