So got my X5 back from the dealer after three days in the service dept. They did take my concerns seriously to do more thorough diagnostics beyond the gas cap, apparently found some diagnostic faults and smoke test leak. They tried replacing one or two things including the sensor, before finding "fuel pump top cover melt through" and "fuel sender melt through", sealed up those leaky areas of the fuel tank. They said they were going to replace the fuel pump as well, but not sure if that was ultimately needed.