1975 Volvo 164 Master Cylinder Problem?

The brakes on my car require excessive pumping to stop the vehicle. At times, they do not work at all. I have also noticed that my gas and temperature gauges are not working. My car has, I think, over 400,000 miles on it and I have no idea when or if the master cylinder has ever been replaced. I was wondering if it actually is something wrong with my master cylinder or whether my car is just old and worn out. Thanks :)