Wrong fluids

Hello, I'm Danny.

Whoops! Let me ask you this first. Have you pumped the brakes and further introduced the contamination into the brake system? Or, did you just add to the master cylinder and realize the mistake? Regardless, The whole brake system is going to have to be flushed.There might be a possibility the brake master cylinder will have to be replaced. Here is a tutorial showing what is involved:

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

The properties in any stop leak additive is to swell the seals to stop the leak but it weakens/deteriorates the seal over time.Get back to me with the questions I asked and we'll go from there.Hope this helps and thanks for using 2CarPros.

Danny-

As Danny says the system will at the very least need to be fully flushed. What brand and type of stop leak is it? The issue is how far the stop leak has gone and what it contains. Some materials will damage any rubber parts in the system and could result in not only replacing the master cylinder but every part that has rubber seals or parts. Doing a conventional flush or bleeding could easily push the contaminated fluid into places it isn't at the moment. To flush the contaminated system you will need to use a pressure bleeder and flush from the calipers back to the master cylinder. If the stop leak hasn't mixed through the system forcing the fluid backwards may save some of the parts.