I followed the only vacuum line I could find out of the master cylinder, which went under the intake manifold, but I couldn't find the booster. Is that the one?

I suspect it is failing as there are occassions that when I step on the brakes it feels as though I am not getting full power assistance. I have to use much more force than usual, and it still doesn't respond as it should. The pads were all replaced last November, and have perhaps 6,000 kms on them. The lines were replaced at the same time with stainless steel, and the rotors are only a little over a year old. I had the brake fluid flushed when I did the lines and pads, and then I flushed it again last month just to be sure it wasn't fluid related.

Thanks for the response,

Jonathan