It's most likely salvageable. You're going to have to clean the heck out of it though. Hose everything down with Electosolve (specifically made to clean gunk out of motors) and wipe it all down. You can also do it with plain rubbing alcohol, although that will take longer to deal with the oil. Keep doing that until it's clean, and don't forget to do the brushes! You can also use a really fine sandpaper (600 grit) to lightly go around the commutator-the copper part-to clean more gunk off. Let the whole thing dry, reassemble, give it some power and see what happens. It should be fine.