The present invention teaches a powered door operator for passenger transit vehicles having a drive nut assembly engaging a door hanger bracket substantially connected to a door disposed within an aperture of the vehicle structure. Such drive nut further engaging a drive screw to move a door for covering and uncovering an aperture for ingress and egress of passengers in a wall of a transit vehicle upon rotation of the drive screw enabled by a rotary prime mover. The drive assembly comprises a housing having an internal cavity, at least one drive nut insert having a helix portion substantially identical to the drive screw helix and disposed within said internal cavity, and a retaining clip engaging said at least one drive nut insert for substantial retainment thereof. Retaining clip further provides for simple replacement of such at least one drive nut insert during maintenance cycles thereby substantially eliminating periodic lubrication generally employed with powered door operators of the prior art.