how can i stop my dryer from staining my clothes??

i called some guys to fix my dryer, and they said, after changing the motor, that i had to clean the inside of the tumble dryer before drying my clothes, and said this was normal after what they'd done, or else they would get stained specially the whites. so i did this, but still, about 8 months have passed and the dryer is still staining my clothes!! i've cleaned and cleaned and i don't know what to do!! i've called these guys and they don't come back, so i'd like to know what i can do!! could this be over with cleaning the motor? thank you!!