The end of the key in the lower picture (which happens to be the engine side clutch half, the one that is prone to the problem) looks as if it might have moved axially toward the thrust bearing and become chewed, which we have seen on other SB45s that had the captive cotter problem. Also, the captive cotter might be pulled through slightly further than usual, though it doesn't look severe.
You haven't posted pictures of the thrust bearing that goes between the two clutch-halves, which seems prone to failing when the loose cotter syndrome appears.
Let's see what Deejay makes of it all - he's been through this with his own mower.
