My Dolphin Premier gets stuck on the drain covers. I took the vacuum to the pool store and they refurbished it, and now it's working better and moving faster and not sticking on the covers as much, but I'm afraid when it gets stuck on the drain covers that causes wear/tear/damage to the vacuum and I'd like to find a solution before the vacuum is damaged again. I'm attaching a photo of my drain covers. They aren't flat and they're about 2 years old. Does anyone know of a part or fix I can use on these drain covers to prevent the Dolphin Premier from sticking there?