Just thought I'd drop my 2 cents on the ps fluid in the master..... I've been a licenced tech for 25 years, ish....
Seen it many times..... Unless there is a dramatic leak that allows fluid to "travel" Realize the fluid as a whole
essentially moves out to apply and back to release.... Very small amount !
Swap out the master & reservoir, Bench bleed it and install ,bleed the system at the lines that leave the master.... Done deal ....
The contaminated fluid typically doesn't get beyond the master itself....
M