I took my 1971 Series 1 auto out for a drive the other day, and the brakes felt soft.  The pedal needed to be pressed down all the way to brake.  I pulled the reservoir cap off and the one closest to the firewall had almost no fluid.  Does this suggest it needs a rebuild, or time to replace?  I cannot find leaked fluid anywhere. If a rebuild or replacement is necessary,  can anyone suggest a reasonably priced replacement? Thanks!

Did you check inside the booster?  The Master-Vac?  That's where fluid often goes when it leaves the MC.  Probably means you need a new MC, or to rebuild it, and want to check the booster well and clean it up.  The brake fluid will damage it.

Look around the insides of the rear wheels.  My '77 is leaking at the wheel cylinder causing a "top off" of the smaller reservoir.  It's hard to see after driving though, maybe put some newspaper down fill it up and pump the brakes.  Check it the next couple of days.  Or pull the wheels off.

Good luck, you'll need those brakes when you least expect it. 

My '72's brake booster went bad, hard pedal, I replaced it and found it was full of brake fluid.  Replaced the master cylinder then.  Brakes are like replacing old plumbing, once you start it all begins to drip somewhere.  

Thanks for all the replies guys.  I'll have to get a good look at it on the weekend. Short days and daylight savings mean that garage hours are cut short in the winter!

It could be me but I was unable to successfully bleed the brakes without adding speedbleeders.

Don't play around around with the hydraulics...it's not worth it

Just one meeting with a telephone pole will cost you 10 times of replacing every component in the system, or worst...

if you have to replace the front calipers might as well upgrade to the toyotas(4 piston), rebuilds are $30 at pepboys, and they will take yours as cores. win win.