Now that my boiler is out and the heating element removed, is it a good time to do some extra cleaning to it? This is what it looks like:

Good question. I don't know what the pros use, but I used what I had on hand: wet/dry sandpaper (probably in 320 or 400 grit to start and higher to finish), steel wool (the bags are labeled with suggested uses for each grade), and/or synthetic steel wool.

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The sandpaper and steel wool leave goo behind that you have to clean out before reassembly. Rinse well afterwards, too.