2004 Jaguar XJ8 - 102700KMS - Vibration in the body from 80km-110kms. Have changed all 4 tyres and balance. Mechanie said that will fix the problem; now he is saying that it may be the drivetrain which he says is very expensive...help please?

Check the u-joints in the drive shaft for looseness or rust streaks. The speed makes it well above harmonic vibrations normally occur. Check rear engine mount for condition and if the rubber is soft it may pay to replace it. The jaguar car rear end uses the two axles as upper control arms and so it may be necessary to check the u- joints here as they carry a lot of load holding the wheels upright while driving the car. It may pay to find a jaguar. specialist workshop because the drive train and rear end are not the same as most other cars and general mechanics will have little specific knowledge to diagnose the problem correctly