2.7 tdv6 servo problem

hi all my second jag is now having a sulk normaly with brakes im ok but this is a bit of a head scratcher
when i push the brake pedle it moves down on its own just a fraction but enougth to make smooth braking impossible and it stickes a bit if i put 1 foot under the pedle as a spring its ok going to give a good lube up and check vacume lines inside and outside but has anyone come accross this before