http://www.roadfly.org/jaguar/forums/

This is by far the best group I know of for owners besides Jag lovers.
Its moderated and divided into subgroups of model types and years.

For XJ40 owners... sometimes you can tap into the knowledge of the 7
series bimmer group as these cars share alot of the same parts and
problems.

Remember to use the search tool to get most answers without bothering
the "elite" members with repetition.

Cheers,
Blake