Fit the circlip to the stub axle, push it into the sleeve, engage the splines then give it a good smack with a soft (copper) hammer.
Oh it is, felt like a bloody impossible challenge. Stick at it and it's doable with patience and take it slowly. It took me many attempts.I'm in the middle of this now. What a shitty job! I'm debating forcing it into a socket then popping it out once it's passed the entry to the smaller area