Battery draining fast

Bear in mind that field resistance changed over the years, and gets lower on some of the late model high output stuff. As long as it's not a dead short, it's probably OK.

The "ultimate test" is to "full field" the alternator and see what it outputs.

If the output is lower than expected, you might have one or more diode gone, or a problem with the stator, or you can even develop turns-to-turns shorts in the rotor, but rare.

Once you've been through a problem like this involving brush holders, you can pretty much troubleshoot them visually.......simply pull the brushes and inspect.

I used to waste NO time in screwing with this stuff. Get the alternator off it it won't cooperate and on the bench where you can see it.