Exactly. Some idiots even block sand their irons. I'm at a loss to understand why, when a simple razor blade, like from a box cutter (because they're thick and pretty safe to handle) do a better job and won't damage the nitride.

On stubbron areas I will grasp the blade with a small vicegrip but you need to be even more carefull because you gain a bunch of leverage and can do some real damage, but if done right can make a tedious job go much more quickly.

Oh and before you ask, on the rotor housing edges, I like to use green scotchbright pads, just a small piece torn off, along the edge where the hard chromed surface meets the aluminum (there is a sawtooth-like formation of underlying steel where it bites to the aluminum youll see under the corrosion). The aluminum is obviously softer than steel and way softer than chrome, so again be careful.

As for the coolant seal grooves, I have a couple of dedicated screwdrivers ground to the right width for the two different groove sizes you'll encounter. Light scrpaing here. Then go over them with scotchbright. Some areas will have so much white powdering aluminum that to clean it all up would dig too deep and ruin the groove, so I do the bet I can. No coolant leaks to report. :)

One thing to avoid is glass beading. The micro pitting allows oil and coolant to have capilary action and eventually will leak out; oil from the pan and corrosion from coolant will be seen on the outside of the engine and builds up over time, especially the oil. I had an engine built buy a shop that insisted on glass beading anything aluminum, that after only 7000 miles, was covered in oil next to the spark plugs. I can dig up a pic later if you want to see how ugly it was.