with regard to fuel ,
the V12 was designed to run on ' unleaded petrol ' of 95 to 98 RON , my 1989 V12 on marelli ignition even has a ' fuel rating plug ' in the engine bay to tell the ECU what RON rating fuel you are running in the car, with the supplied plug fitted or not fitted allows a different map for the ECU to prevent detonation issues etc , mostly for the continent and US fuel which is rated lower I think ?
so , in the UK at least, ' normal ' unleaded is fine all the time, but high rating unleaded can be used , and some benefit can be felt when doing so ,
but as with any V12, you need to drive it like you stole it to ensure it is happy , don't trundle around just above idle, let it see the red line.........
1994 3.2S in Morocco red and Doeskin/Ruby red interior
1989 V12 XJS White with Mulberry interior
2004 2.1 X-Type Platinum with Sand interior
1999 V8 Sovereign in Seafrost with Oatmeal and Antelope interior