How likely my rear brake line is leaking?, brake fluid in the channel and under drivers seat Options

[boxster914]

Long story short: my brake pedal went to the floor, I noticed the rear fluid reservoir was dry and my drivers side floor pan full of brake fluid.

After doing some research here at 914world I decided that the master cylinder died and it needed replacing.

During the install of the PMB 19mm master cylinder (oh what a pain that was but thank you again to 914world in helping me seat the supply lines) I saw that there was brake fluid under the drivers seat. This was strange because there is a ridge separating the front and rear sections of the floorpan so I couldn't figure out how the fluid would have collected under the drivers seat.

A little more looking and I see that it is wet in the channel with a deep puddle of it settled at the rear firewall.

So the fluid leaked from the hole in the channel into the pan area under the drivers seat.

So now I'm putting this all together:
-rear reservoir compartment dry (supplies the rear brakes)
-lots of brake fluid in the channel

It seems that the fluid is leaking from the brake line that runs in the channel and not necessarily the master cylinder failing.

What is your take on this mystery?

If it is the rear brake line that needs replacing how the heck do you do that?