Accidents happen. With condenser lenses, that usually means a scratched or chipped lens. Small chips right at the edge of the lens and very minor scratches probably won't have an effect on the prints, but major chips and scratches might, in which case you need to replace the damaged lens.
As selected below, these are either brand new OEM condenser lenses or used condenser lenses in perfect condition - no scratches or chips which effect their intended use. They can be used to replace main 6½" condenser lenses, upper or lower, in all Omega D-series condenser heads. Two are required for a full set.