Been there, except it was my in-laws’ back door that turned to mush after years of rain hitting a bad seal. We kept patching it with filler but every winter it got worse. Finally called a company that handles both supply and installation so we didn’t end up with blame games between separate crews. They came out, measured twice, and actually pointed out where the water was getting in so it wouldn’t happen again. Happy we went that route, door fits properly and no more drafts. If you want the link, this is who we used: door installation West London . Not trying to sell anything, just sharing.