Ignorance is a bliss
Because I've noted my brake pedal is not as firm as 11 years ago, I was thinking to change entire cylinder (I have only one car so I have to anticipate doing some preventative repair)
I was unsuccessful trying to disassemble GD3 Fit brake master cylinder, until I found instruction for 2003 Jazz. So I went to the junk yard to see if this instruction will work on GD3 Fit and to examine the internals of the master cylinder of neglected brake system (I've changed brake fluid 3 times, but, of course, these were only "partial" changes, not full flushes.
So let's go

A nice car

Taking out the master cylinder...

Removed already. (Note, there is no gasket or seal between the cylinder and the booster)
Next step is to remove 8 mm hex screw attaching the reservoir to the body and pry reservoir out (I drained it into the washer tank

This pin (red arrow) keeps the front piston in, similar to the external screw on older models. Note the green, oxidized (?) brake fluid!
After pressing the rear piston about 1/2" in , the pin has no tension and falls out, once cylinder is placed upside down; taking the snap ring from the end allows both pistons to come out straight and square without marring the inner cylinder walls.
The piston cups were in good condition, no abrasions and tears as well as cylinder walls!
This finding gives me opportunity to rebuild my own cylinder after finding appropriate 7/8" cylinder repair kit
This practice worked on my 87 Camry with sinking brake pedal and the "desperate" repair has lasted for 9 years from (2005 to 2014) when I retired it
Two more pictures:

Loose spark plug went undetected and stained a coil!

Honda engineering mishap: new genuine pad was not matching new genuine Honda rotor; the pad was a bit wider and overhung into the hat area making small ridge at the edge!

Sorry for picture quality ,my old phone camera is not as good as the new one

 

Hey---I go to my local Pull and Pick here in San Diego too. Love the place but now that I'm running this "luxury" model of a Honda Fit (fun) it now costs me five bucks to "window shop" instead of the three bucks I used to pay at the door. Anyway, I find it good to check their online inventory before heading out, to see if the cars they just got in, might have an undamaged part I need----usually cosmetic. I've been watching for both fog lamps (can't imagine how the previous owner broke both) but I was told the car did have a front collusion by the first owner so he must not have ever fixed. Anyway, I have a good time finding the things I need at my local pic & pull, especially on their sale days. Thanks for your post and good luck.
Jerry