How to test a brake servo?

I was reversing slowly down a slope to park a couple of days back and the brake pedal went slowly down to the boards and the car kept moving slightly.. There was a strange noise (gurgling!) from the servo/master cylinder area which hasn't repeated. Just towed a caravan 15 miles..
The pedal 'pumps up'. Typical leak or worn seals?
Can't find a leak, reservoir is full, fluid changed within the last year. On another forum someone suggested a servo fault, but in my experience a duff servo means a solid pedal. Have a master cylinder coming in the mail, main stealer has a servo for me at £150 , but I'm not convinced the servo is faulty. Anyone know of a test for the servo which will show me if it's faulty? Should I simply replace them both and sod the expense? Thanks for any reply..

a faulty servo would not allow the pedal to hit the floor you would just have to press the brakes alot harder to get them working. it sounds like the seals in the master cylinder are shot causing fluid to make its way back past them not actually pushing the fluid. or rather unlikely your rubber brake hose walls have deteriorated allowing them to bulge but it would have to be 2 or more of them in order for the pedal to reach the floor.

to check your servo with engine off pump pedal untill it goes hard keep your foot on the pedal and start the engine, you shoud feel the pedal go abit softer, showing you the brake servo is assisting.

hope this helps, Dan

Thanks Dan, I was in my nearest stealer's today and like a techy at my usual servicing garage, the workshop foreman said he had never known a Disco 3 master cylinder needing to be replaced.. I am coming to the conclusion that's the problem though... I get your meaning about the flexible hoses because of the dual circuits.

We once went to look at a 3 year old 90 and went for a test drive. The guy lived down a 300 yard long lane off a main road. Going quite slowly I started braking for the main road and the pedal was rock solid! I had my backside off the seat, standing on the pedal and just stopped as two 40ft artics thundered across the front of us.. I took it back and asked the guy if he knew the servo had gone..
He said no.. and thought 'all Land Rovers had brakes like that.' he'd had it from new and some of his employees drove it regularly.. And hadn't noticed anything wrong! He got it fixed under extended warranty and I bought it, but next time I try out a car privately I'll be a darned sight more careful.