Or, if you're really brave, disconnect the master cylinder to see if the rear seal is leaking into the vacuum booster.

But it's not going to be easy or fun.

 

My fluid loss turned out to be a loose bleeder in the rear. It was only loosing fluid under firm breaking which I try to avoid in my day to day driving so I was not loosing a lot of fluid. On the bright side my brake fluid has been flushed

 

Did that take two years to find? Dane

 

Thankfully no, but I found this thread again and thought I'd give everyone a good laugh

 

I've gone to follow up with threads and couldn't find them!
Thanks for the follow up , and conformation of your findings!
My issue was the cold and the master cylinder reservoir.