I have the same planer, and the way to keep from having to turn the armature is to replace the brushes before they fail. The basic coil and field in this motor is one that has been used for many Delta products. There is a flaw in the windings of a few armatures. The ends are pinned instead of being soldered to the contacts. An unusual electrical stress (such as a failed brush) can cause the wire to burn out of the contact, requiring rewinding. When this has happened, it will eat brushes fast, emitting a nuclear looking blue light around the brushes and chunking carbon dust. Oddly enough, the newer (cheaper) motors apparently don't have this problem.
Having taken both motors apart, the older one is built like a tank for a universal motor. The newer one has half the shaft diameter, and smaller bearings mounted into plastic casings. It looks suspiciously weak for something like a planer.
For about $100, you can get the armature rewound and new bearings, provided you do the motor disassembly/assembly yourself. If your budget is limited, this is the way to go. A properly rewound armature will last forever, limited only by the contacts wearing thin. Keep a spare set of brushes around, and when they only have about 1/4" of carbon left, replace them.
If you have cash to burn, get the Dewalt 13", 3 blade, 2 speed. They rule.