Being a rover i wouldn't bother, simply because it is a rover.
As for the MOT thing they would not have checked for radiator or oil leaks as the mot simply determines if the car is safe (brakes, tyres, suspension etc). However if they were that bad then surely they would have noticed them.
Get a second opinion is always the best option, although to check for leaks park it with some newspaper under it overnight, if there are no leaks then chances are they are lying to you