I don't know how old the worm is because I bought the whole refurbished unit in 2004. But I can tell you this, its welded together in 3 different spot and there hasn't been a sharp edge on it since i've own it, and there is plenty of fines, i always thought it was coal dirt. I've never messed with the air settings. As far as spots, it does spot on full burn, but any other time it only burns the back 1/2 of pot. I punch out the grate holes every summer when I shut the boiler down. One of the grates has developed a 1 inch whole in it over the winter, but i dont think that has anything to do with it since it always does this when i burn poor grade of coal. While I'm on the grate subject, where can i find replacement parts for my efm? Thanks for your speedy reply's fellas.