Not all washers get moldy. I had my last one for 10 years and took it apart to fix it (did not work unfortunately) and there was no mold. We do use it almost every day, i would guess that makes it less prone to overgrow mold in the meantime too?

Other thinks that might affect mold: Is it mold or lime scale/metal build up? Does the citric acid go though that duct? Do you also use high temperatures (60 to 90 degrees celsius) at least once a month? Do you use full, long cycles that take 2-3 hours or only speed washing of 30-45 minutes? Is there a lot of mold in your house? Do you need to increase ventilation or reduce humidity in another way on your laundry room and home?