can u hear any air leaks in the engine bay?
is the pipe from the servo to the inlet manifold in good condition/ un damadged?

servo is a piece of cake to change any way, drain off fluid from resivoir then unbolt master cylinder.

theres four bolts at teh back of the servo take them off, get some one inside the car to press teh brake pedal this will push the linkage that connects the servo forward so u can pull the split pin out of the connecting rod then remove the little plastic pin, u may have to bend the drivers side bracket over a bit to get the pin out.