That's the one! I'm not as fussed about the loose-ness - I quite like being able to have it high out of the socket and able to rotate it out of the way when I'm not using it, but I'm sick of the arm falling out completely.
There are replacement collet/bushings but it looks like even the AVRI pieces have the same arrangement of four teeth
that the CIJ parts have. The AVRI trems are supposed to feel more solid and smooth udirng use, but the arm will I think still work itself loose over time.
Sounds like I'll be doing an AVRI upgrade to my trem assembly, and swapping the arm and bushing for the Staytrem soon after. £30 still sounds like a lot, but it's worth it if it works.