Actually, it didn't matter if the tube was on or not when you used the drill by it. It magnetizes it either way. (When it's on, you just have the ability to see the effects immediately)
The degaussing coil around your tube is there and works automatically every time you turn on your monitor from a "cold" start. (e.g. like after it's been off at least 5-20 minutes, depending on design). That's why most computer monitors, when first turned on give a lound "thunk" sound and the screen wavers a bit. That's the monitor sending 120 volts thru that coil to help remove any magenetism that built up on the metal mask. (side note: This gets built up normally just because of the earth having magnetic poles. However this is a minor amount and not like what you did by putting a large amount of magnetism towards one side of it)
My FIRST suggestion is to simply turn on the monitor, then turn it off, let it sit off a good amount of time to cool down the circuitry that activates the degauss, then turning it on again. Basically turn it on, then off for 15-20 minutes (or longer, depending on monitor), then back on. Do this for a day or so. See if it makes the color/bending less in that corner.
(You see, it works by sending a ton of volts through the coin when first turned on, which, in turn increases heat in a resistor. This resistor shuts down after a few seconds, but must cool completely, and be activated again when it turns on the next time. Without this circuitry, it would constantly be degaussing the screen, causing it to wave and change colors while you used it (and heating up the coil like a light bulb and burning up besides!
))
If this doesn't work (assuming the circuitry is working), then your next step is to get a separate degaussing coil or find someone (or buy) a Bulk Tape Eraser like from RadioShack, sometimes you can find them at thrift stores too for a few $, I know one near me had one a few weeks ago for $5.
Follow my instructions in the previous reply on how to use an external degauss coil or tape eraser. You might want to also check out Bob Robert's instruction pages (
www.therealbobroberts.com) and click on "you need help" link at the bottom. I think he talks about how to manually degauss things.
Finally if all that fails, try the magnet trick. Start first with something small, like a small poster magnet or fridge magnet instead of the massive speaker magnet. Then you cant ruin it too much, but it might not remove it all. Yes, you CAN screw it up so bad you might not get it out... However, I've gotten some bad bending/color problems fixed by using a broken sliver from a ring shaped speaker magnet (about 1/6 th of it's size) on a 19" arcade monitor a couple times. If you go too far in one direction (e.g. turning purple to green), simply flip the magnet over to use the other "pole" and then undo it the other way.
Good luck.