The factory fitted seal is poor design and quality and within just a few years from new it begins to break down. This is a problem because as the seal begins to crack and fall apart, air begins to leak into the fuel tank triggering the EVAP warning system (common fault codes for this are P0455 P0456 P0440 P0442), the cracking of the seal would also allow fuel to escape if the vehicle is overturned hence the MOT failure.
