Three WF class flat wagons (30035, 30043, 30054) were converted to class WFM in January 1973. WFM 30035 reverted to WF in July of the same year. However, WF 30018 became a WFM in 1974. WFM 30043 reverted to WF in 1975 followed by WFM 30018 and 30054 in 1976. They clearly weren't a great success.