It's worth every penny to take it to the dealer for this. Tell them of your repair, and that you have no idea how long the current brake fluid has been in it. Have them use their machine to R&R the fluid and you'll sleep so much better.
edit; I just looked up what I paid and on 12/28/18 it was $129.96 for "Brake flush and exchange".
edit; I just looked up what I paid and on 12/28/18 it was $129.96 for "Brake flush and exchange".