That's really helpful, thanks, and gives me the confidence to go at it with the file! Many thanks for the prompt response.

Hi all
After some hunting, I finally acquired a lovely 1968 Lettera 32 in great original condition. The only issue (apart from the rubbish PVC case...!) is that the lower case q doesn't fully hit the platen, the bottom of the letter is missing completely. It sounds different to the other keys too, as I assume that all the force of the key strike is going into the segment plate (not the platen). There is a similar issue with the last key on the opposite end of the segment. I've had a close look and used a feeler gauge to check the gap to the platen when the key is fully pressed, which confirms there is a greater gap, compared to other keys. Bending the slug forward would just cause the top of the letter to hit even earlier, still leaving a problem with the tail of the letter. The only logical solution is to file down the lug on the typebar arm, so that it hits the segment plate later and hence the slug gets to hit the platen properly. I'm reluctant to make this non-reversible adjustment in case I'm missing something obvious. It's slightly better on upper case (Q) but still a little faint.
Any thoughts?

Nevermind, I got it. it unscrews as long as the platen is held stationary but I had to REALLY twist on it hard.