Brand new first motion shaft for 4 synchro pre-A+ gearboxes using the later 18mm noses. This gear was used in all 1275GT gearboxes from about 1979-81, and has 18 teeth and has no grooves cut into the teeth. Earlier pre-A+ gearboxes used a similar gear but with a narrower 14mm pre-A+ mainshaft. The 1st motion shaft serves as both fourth gear as well as the transmission input shaft, and recieves alot of abuse. If a bearing in the gearbox fails then this shaft can get destroyed quickly. 
 
Often times a crunch while engaging a gear is a result of a failed synchro ring, however if left ignored the gear and selector will start to get damaged. If you see any chipping or broken selector teeth, pitting on the synchro surface, or any wear on the actual helical teeth, it is time to replace the gear.