Change
The easy answer first. Scott, remove the Mixfinder dial and be sure to keep the washers in place on the dial. Remove the condenser, large waxy tube thing on the bottom of the speed switch. Replace the dial and the mixer will most likely be fine. You can source a new condensor if you are a purist, but the mixer will work fine with out it. Other more serious options are new switch or replace the governor tension rod. Remember with the vintage Sunbeam, lubricate, lubricate, lubricate. You will end up with a screamer if you don't.
Sunbeam began to reduce the quality of materials in gears, spindles, windings, housing, cords etc, until the weight of the finished mixmaster was 4 pounds less. The switches were under engineered for the higher wattage motor and stress of heavy dough and bread. The gears stripped, they were loud and vibrated, the turntables came loose from the spindle and those were the main complaints. In 1992, Sunbeam, Australia began making the new motor and design. It is nearly silent, very powerful and an excellent mixer except it is laden with push this and pull then to get the mixer up and down from the bowl. Most won't come off the stand and the newest has such a flimsy handle it will break if you try to use the mixer portably. They have an internal fuse, integrated into the swith so if it gets to hot or burdened, the switch goes and you are mixerless. That said, the Australian innovations to Sunbeam may give it a chance as survival.
Nothing ever mixed and creamed like Sunbeam BowlFit beathers. The finished products have a much finer and lighter texture than the more crude paddles used in mixers with planetary action.
Kelly