A sander that size probably has a universal motor. Depending on the machine, it may or may not allow access to the brushes. If so I would remove the brushes and blow out that area to be sure it is fairly clean. If it is of the heavier breed of these handy small sanders (cast iron body, replaceable platten and so forth) I would forge ahead trying for a manual, parts list or even a repair shop. If it is of the stamped steel, 20 pound, no-name family of these machines I would probably scan garage sales for a used one to replace it and move on. You may be surprised how easy access to manuals and parts are for some of the darndest things. I have gotten help with things I thought were definite throw-aways so, punch in the model and make if you get a chance. It may live to fight again
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke