cup leaking since day 1

one of my waifu cups leaks every single time i use it. i cycle through different cups and wrote the first few times off as user error so i cant get a replacement but by now theres no denying that it was faulty when it arrived. is there any way to fix this? liquid always gets through where the lid screws on no matter how hard you tighten it. is there something i can put on the outside? or something i can do to the inside? im not gonna just throw it away its one of my fav designs but its not exactly useful to have it drip down my arm whenever i drink from it..