Does anyone have a part number for the rubber seal ring on the fuel sump tank inlet? Any chance it's the same as the one on the gauge sender?

 

It is the same as the guage sender. Part numbers can be found easily on this site, by the way!
https://parts.jaguarlandroverclassic.../brand/jaguar/

It is number ARA1502J and is found here, see diagram number 17:
https://parts.jaguarlandroverclassic.../brand/jaguar/

A search reveals loads for sale:
https://shop.everydayxj.com/XJ6_XJ12...4-ara1502j.htm

 

Thanks Greg. Car ran fine when I parked it last fall but the second trip out this year it refused to start after putting fuel in it, acts like it's out of fuel. The fuel pump runs but I'm going to check the fuel pressure at the rail. I suspect the filter in the sump tank is plugged, when I changed the sender last year it looked pretty ugly inside the tank.