I've had the chance to take a better look today and I'm 95% sure it's the rod in the rear n/s shock rod that is banging against the side of the top mounting hole (diagram from Haynes manual):

The grommet shown in the diagram has all but disintegrated (light brown item in pic below), so allowing some sideways movement:

The shock itself, although manky, still appears OK, albeit the bottom bush is showing some signs of age. I’m torn between cleaning it up, sorting out the “grommet” and putting it back on. I’m thinking I might put an “O” ring or two in place of the grommet?
Alternatively, I have a pair of brand new KYB shocks that are meant for KIMI 1, so reluctant to use those in case I have trouble sourcing another pair. Also, here is a picture of the KYB shock and fixings, but it doesn’t include a grommet either?

Has anyone got any thoughts before I put things back together?