I've done only the Essentials course and am looking for a job here in Tucson (freelance will do), and so in the mean time I've been copying/drawing some things.
WELL I just learned that if you unclik the Merge box in the Extrusion tool the new extruded part does not 'merge' with the old one and there is a line..... DUH!!!! so I guess I just need to keep on cliking and uncliking.... points