Took apart the 3/8"er. Grease was old and dirty, brushes were dirty, and a bit of stuff had infiltrated the mechanism. One set of windings around the motor looked a much darker red than the other - could have been overheating, but there's nothing I can do about it now.
Soaked and scrubbed both body shells, soaked the bushings in Supco, and carefully cleaned the brushes. Put a nice glob of Superlube grease in the gear section, and put it back together. had a spare rubber chuck key holder and side handle, so hid them in the box. Sounds great, runs smooth, and no burned smell.
Though, I was not happy to see this inside the case shells.