I cleaned out my keystoker A120 last weekend, and found quite a bit of surface rust on the heat exchanger, and in the firebox. I think my biggest mistake was not disconnecting the stove pipe and cleaning the furnace immediately after the heating season. I got it cleaned out very well, and left the stove pipe disconnected (plugged the thimble) and am running my dehumidifier 24/7 with the stove doors and flue open. The grate and pusher mechanism look perfect, it's really just the heat exchanger and firebox walls that got surface rusty. I got as much ash out as I could, I think trying to clean around in the heat exchanger area with baking soda and water would be a complete and utter mess though. It's very hard to get in there. I have a can of the CRC 350, would it do any good to spray it on the already rusty areas? Should I scrape the flaking metal off of there first?