Well, I'm 90% through step one - an upstairs toilet which had a leaking valve and needed a new flush assembly. I change the flush assembly to the dual-flush one, changed the valve...and while trying to snug the valve using the original compression fitting (as per advice of the plumbing guy at Home Depot) . broke the damn pipe off!!
Scrambled to turn water off while there was a geyser in that bathroom. Found that there was still enough copper pipe sticking out of the wall for a valve re-fit, so I filed the end square, sanded the copper to get a clean surface, and successfully installed a new valve to provide water to the toilet.
Now the new toilet flush mechanism is installed but the flush control portion that replaces the flapper isn't sealing right and the toilet periodically re-fills. I can sort that out later.....
Now I have the bad toilet in the basement out and need to either remove the rest of the existing cast iron toilet mounting flange or find a "spanning strip" to replace the broken out bolt mount before I can install a new Kohler. I'm researching how to deal with that flange.
Just to add the general fun, we've discovered that the water in the carpet didn't come from the toilet, but from a boxed-in drain pipe that carries greywater from the top two floors of the house. It apparently has been leaking slightly for a while, but got bad enough to notice in the past couple of weeks.
THAT is a plumber job. I'm not going to mess with it. I hope the problem is only on the lower end where we can reach it, but if not, I think we'll be opening up a wall directly above the point where the dampness is. We have determined that we can't use the master bath or guest bath sinks upstairs, nor the kitchen sink or either shower on the upper floors - fortunately we have a basement shower that drains through a separate greywater pipe. May be eating out a lot for a few days.
Oh oh....My wife just said she feels water on the back side of the pipe above the leak we saw.
Nothing money can't fix, I'm sure.