Matthew, with all due respect to you, from a certain perspective, you've been your own worst enemy here. you came onto an open public forum on the internet, and you explained thoroughly, and in pretty good detail that,
1. You have a vehicle that you are selling, that has an issue that affects the safe operation of that vehicle.
2. You wanted to try to perform the quickest and most inexpensive repair that you possibly could, regardless of whether or not its a proper, safe repair.
3. That you wanted to do a DIY repair, even though you really don't have the tools to do a proper repair, and that you have limited knowledge and skills.
You have received some good advice from a number of people, who do have both knowledge and experience with situations like this, and repairs like this.
While I do hope that you are successful at getting the repairs done on the car, and getting it sold successfuly, I have a bit more advice for you, for whatever its worth. Either stop right now, and leave the car as it is, and sell it as it is, and make full disclosure of the issues with it, to any and all prospective buyers, or find someone with some experience and/or qualifications, who can do a proper, safe repair, before selling the car. I've been a licensed mechanic here in Ontario Canada for almost 40 years now, and I've seen my share of situations like this over the years. Although I hope that you're correct, in that the rest of the brake hydraulic system on that car is in good condition, it would not surprise me if you run into other problems in the course of completing your repairs. Good luck, and please let us know how it works out.