(Posted in 2 parts):
Leaking brake fluid isn't that easy to spot on a cursory examination. I once had a problem with 'soft' brakes on my car. I took it one of the big companies that deals mainly with tyres, brakes and exhausts. They took the whhels off and diagnosed worn brake pads, which they replaced. When I drove away, the brakes still didn't feel much better. I took the car to another (similar) company, to take advantage of their free brake check. They couldn't diagnose the fault. Eventually, took the car to a firm (KwikFit) who said "We don't do free brake checks because the only way to really check brakes is to take the whole assembly apart. We charge �20 for that but we refund your money if we carry out any repairs". It was only then that two leaking brake cylinders were discovered.
My point is that leaking cylinders can be hard to spot. All that the MoT test involves is a quick visual check (without taking the whole brake assembly apart) and a check (using a rolling road) that the brakes meet the minimum standards for efficiency. As long as the car gets through the rolling road test (and there's no problem with the visual test), it will pass that part of the MoT. (Even if the examiner can see that the brake pads are low, he'll still pass the car if it can get through the rolling road test).