Overheating Edger Motor Brushes

I've got a B&D Edger that I bought used a while back. Other than having to replace the spindle gear once, it's worked well over the years.

Shortly after I replaced the spindle gear, the edger stopped worked - although I'm sure the spindle gear replacement (mechanical fix) has nothing to do with the motor (electrical problem). I pulled the motor cover, and pulled the brushes and brush holders - and they both looked like they needed to be replaced (they were probably the original brushes). I bought a pair of replacement brushes (for $2.65 each) and installed them. The edger ran fine, but only for a short while and then it shut off.

When I pulled the motor cover and the new brushes, it appears as though the were exposed to a high heat condition and looks as though the distorted/melted - including the hard plastic holders, almost in the direction of the spin of the motor.

I noticed that the armatures appeared appeared to be pretty tarnished with carbon (and whatever). I subsequently took the step of repolishing the armatures and getting them back to a mostly original state.

I've now got a set of replacement brushes and holders being shipped my way - but was my problem (probably) the a contact problem between the brushes and the armatures, or should I be looking at something else before I install (and maybe ruin) another pair of brushes and holders? Thanks!