Could be one of a few things possibly.
Dribble from the master cylinder cap is part of it. Because when you apply the brakes, it puts pressure on the cap, when it leaks, you're losing valueable pressure.
possible that brake lines are flexing from being over 10 years old. if they are rubber, could be time for replacement.
I see you said "Shoes" I'm assuming you have drums then.
It could be the fact that drums just don't have the stopping power like a nice rotor/caliper style