I have had this reservoir for our big dog fountain for about 7-8 years. The gasket shrunk and wouldn't fit within the first year. Unlike prior review though the gasket isn't needed with just common sense. You can go to home depot or so and find a gasket that will fit. Our just do what we have done all these years: fill the reservoir, close lid, carry it to the dish, tip it over and put it in. It doesn't leak and drains like normal only as more water needed in the bowl.
A manufacturer who sells a product that depends on a gasket to prevent leakage should be required to sell gaskets separately (single or multi-pack) and should not require the user of the product to purchase a complete reservoir. Also, a Petsafe customer service rep should not argue with an engineer with an MS degree that other causes of leakage are more common than gasket leakage and thus the replacement strategy is perfectly reasonable. Citing economics might be more convincing, although there seems to be no problem with offering a $2.50 plastic flow control kit as a replacement part. Why not a 3 pack of gaskets for a comparable price?