A conveyor-type warewash machine includes a housing through which racks of wares are passed along a conveyance path for cleaning. A rack drive system includes a rack engaging structure that moves back and forth in first and second directions. When moving in the first direction, the rack engaging structure moves an adjacent rack forward along the conveyance path. When moving in the second direction, the rack engaging structure leaves the adjacent rack substantially stationary. The drive system is configured to move the rack engaging structure in the first direction at a first average speed and to move the rack engaging structure in the second direction at a second average speed. The second average speed is faster than the first average speed so that the adjacent rack spends more time moving forward than being stationary. A seal assembly may be provided about a drive shaft of the drive system.