Generally speaking it is the responsibility of the owner to ensure a car is fit for its MoT, and in the event of an MoT failure it is the owner who will need to pay for the required repairs. The only potential grounds on which the seller, assuming it is a dealer, is responsible, is if the MoT failure is the result of a fault that was present when you bought the vehicle. However, if that were the case we would expect the owner to report the issue to the dealer as soon as it occurred, and the amount of time that has passed would not go in your favour. Legally, an MoT certificate confirms that at the precise time of the test, the vehicle met the minimum environmental and road safety standards required by law. It is not a test of quality or mechanical reliability.