I did my MECR on the Seneca too. The questions I was asked were all very straightforward and could all be found in the aircraft handbook. You need to demonstrate to the examiner that you have an apppreciation of the systems on the aircraft. The questions I was asked needed me to know the type of flaps on the Seneca, the maximum fuel on board, how the heater works and which tank feeds the heater amongst others. Basically read the pilots handbook and use some common sense and you will be fine - do remember though that you are being tested for a multi engine class rating and not just a Seneca rating so some of the questions may be concerning the class of aircraft rather than just being Seneca specific.