1981 Mercedes Benz 300sd transmission and vacuum pump question

1981 Mercedes Benz 300SD mileage: 220,000. I want to change the transmission filter and pan gasket. Because of the mileage and I'm not sure when or if the prior owner changed fluid. I am afraid to have fluid replaced. Present fluid is clear and unburned, should I change it or will someone just change filter and gasket. Second question, vacuum motor in trunk that runs door locks and gas cap cover, quits after about two weeks. If I pull out, disconnect, and then connect three-prong electrical connector, it works for another two weeks. However, I believe that if I disconnect the vacuum line to the motor, it works for unlimited period.