[ROVERNET - UK] OT - Info on XJ6 series 3

[Damien]

A friend has a 1982 (I think) Jaguar XJ6 series 3, 4.2 litre and fuel
injected. It is in Brisbane Australia he is now running it on Premium
unleaded and using the valve additive. I was wondering does he need to use
the additive or are the valve seats ok to run on unleaded?
If no one knows for sure does anyone know where I might go to find out?

Regards

Damien