Hard or notchy shifting, especially down into second once the box has warmed up, usually comes from worn synchro rings – and it's one of the most common reasons to split an M40 or M41 on the 122. The M41 is the same four-speed box as the M40 but with overdrive added, so most of the internal wear parts are shared between the two versions.
This group covers synchro rings, ball bearings and lock rings for the gearbox itself, plus the screw, washer and spring washer that go with sealing and reassembly. For the shift mechanism there's the gear lever gaiter and the gear shift lever knob, parts that wear or crack over the years and are often replaced at the same time the box is rebuilt.
During a rebuild, the play in the ball bearings and the condition of the synchro rings are the natural points to check – worn bearings show up as a whine and quickly lead to knock-on wear. This category gathers the wear parts for that job, not complete boxes.