This may help a little until I find better. "Fittings" leaking, meaning the brake line attachments to the master cylinder could be leaking. Just wanting to be sure there is not a leak that is flowing from somewhere and dripping off the boot. If it's coming from inside the boot, it the internal piston seal.
We all have made many mistakes along the way. Now you know you have to inspect the piston bore, hone it if it's savable and be real careful on reassembly. If you don't make mistakes, you are not doing anything. It is possible with Chinese rubber parts, that they have low reliability and short longevity.
It is also possible, I think, to use the wrong brake fluid on some rubber parts.
