Ford uprated the vacuum hose on the 4.6.
Hava a look at your engine and if you have the soft elbow going from the PCV-valve to the vacuum tube that connect with the T/B, this is a worthwhile upgrade.

It prevents a vacuum leak that caused me 2 day of a headache

Now at reduced price at SMC
http://www.ebay.co.uk/itm/Rover-75-V...item19da7e973c