A leaking check valve isn't all that uncommon. Happened to us on our brand new TT. Does it fill up slowly or quickly? If slowly, it'll be the check valve at the pump. You have a couple of other options. Install an additional check valve at the pump by using a quality, commercial grade, brass body one and leave the existing pump & check valve alone. Or if you won't be using the FW tank much or never, install a shutoff valve at the pump which is what I did. A valve or check valve could be added using a sharkbite type. Cut PEX & insert pipe - done in under a minute.
Sometimes it's better to just do things yourself, besides you can often do a better job anyway... Also, your TT could sit at the dealer for weeks.
