After troubles with fueling, rough running, and loss of power, I have changed back to original factory plastic air filter box with the paper element. I did have a well-known brand of pod filter, but I found it seemed to let the air flow meter hot wire gum up, and affect running. This would come right if the AFM was cleaned with air flow meter cleaner spray. I think the pod kept small children and birds out, and thats about it.
I have noticed no loss of power by going back to factory spec filter, and I think its a good decision for me.

I also had some horrible rattles and clanks coming from the front end on bumps and potholes. I tightened a loose headlight and relay, removed some plastic covers from around windscreen reservoir etc, but then found the air con condensor was really loose. New bushes have solved that.
My mechanic told me that 2 of the bushes (I think lower two) are the same as some Mk II drivetrain mounts! Jag must have had some 30 year old spare bushes lying around in the 90s when it came to the X300...