Yay, Jon! Glad you had a spare. I only had some NOS hubs and knobs/clips on hand.
Looks like this washer is an NB, which looks as if the rev B models have the updated timer with the plastic hubs (WH1X2188) vs. the rev A with the metal hub (WH1X1941) - part 7 on the diagram.
While the shaft is then dependent on being either a metal or plastic hub, the detent pin - part 11 on the diagram / WH1X1498, is the same on both and I bet that clip is missing/broke.
Ben