The master bathroom toilet(Bristol Bay) will continuously run water if not flushed just right. Will this replacement help?

I just saw this question today so it is Probably too late. But the answer that I saw that yes you can replace it with a whole new one. Or there’s a real good chance that is is the gasket that you could buy for $2.98 and it is all a lot quicker and easier than replacing the whole thing. 99% of the time that is what it is. But they would rather you go out and buy A whole new assembly.

This issue sounds like it may be related to your flapper. Check and make sure the flapper is closing fully when the toilet is flushed. However, the fill valve may simply be not shutting off, and overfilling the tank. If that is the issue you're experiencing, then yes, a new fill valve would help with this issue. Feel free to contact Fluidmaster's Technical Service Department for additional help with your question. We are available Monday through Friday from 5:30 AM through 5:00 PM Pacific Standard Time. Contact options include: Chat www.fluidmaster.com/support E-Mail techsupport@fluidmaster.com and Toll Free 800-631-2011.