In 1986 conversion of thirty-five WO class wagons to WOC class started.

1986	31203, 31208, 31210, 31211, 31215, 31223, 31224, 31233, 31237, 31239, 31240, 31242, 31246, 31255, 31262, 31265, 31267, 31268, 31269, 31273, 31276, 31278, 31279, 31281, 31284, 31286, 31287, 31295, 31296, 31298, 31301, 31401, 31407, 31408, 31411 to WOC
?	WOC 31208, 31210, 31239, 31262, 31273, 31295 to WO WO 31231, 31254, 31256, 31264, 31275 to WOC WOS 31250, 31270, 31277, 31402, 31409 to WOC
1990	WOC 31251 to WOG
In 1994 most of the class reverted to WO but new examples were built in 1998.
1994	WOC 31208, 31210, 31211, 31215, 31223, 31224, 31231, 31233, 31237, 31239, 31240, 31242, 31246, 31254, 31262, 31265, 31267, 31268, 31269, 31273, 31275, 31278, 31279, 31281, 31284, 31286, 31295, 31296, 31298, 31301, 31401, 31407, 31411 to WO
1996	WOC 31203, 31250, 31255, 31256, 31264, 31266, 31270, 31276, 31277, 31287, 31317, 31402, 31408, 31409 written off
1998	WOC 31341-31357 (Portman mining) and 31358-31370 issued new.
The new build wagons 31341-31370 were still intact as a group in June 2010 apart from 31345 which had gone.