Just returned from the dealer having a deisel leak at the tank investigated, I'm informed that the problem is a 'rodent infestation' on top of the tank and it/they had knawed thro' the plastic elbo on top of the tank.
Had a look and there was certainly plenty of leaf debris there and signs of abbration to the elbo.
But I'm no expert. Dealership stated they have seen it on 3 other ocations on RRS, RR and Disco.
Soloution is apparently a new tank.
Comments welcolm.

It is indeed a known problem- do a search on the D3 site for tales (?tails) of woe.
I had a new tank installed by way of an insurance claim, but I know of one fix being Tiger Seal on the hole. Workshop time was two hours, and bear in mind that dropping and re-affixing the tank may loosen the sender units inside, so check gauge readings before and after the job.

Many thanks DrLex.
It seemed up there with alian abduction.
I may need to apologise to the dealer.

You're welcome.
If you do go for a repair, put something noxious over the remaining part of the elbow. I'm led to believe that the current tanks have a less tasty construction. Don't put the Warfarin-based rat poison out- I had a thirst-crazed mouse drown in the water bottle of my 60s British sports car, but not before it had gnawed through an elbow on the fuel line. Forty years hadn't changed the problem...

Hi,
Had the same problem when I bought my 56 RRS HSE I filled it up at the station on the first day for the start of a test of how much fuel I could get in, to my horror the fuel was coming out faster than it was going in. I instructed the garage to have a look and it was discovered that there was a hole in the top of the tank. The garage I bought the car from said they would repair it using a plastic welding technique which they did. The only issue I have now is RR warranty will not warrant the tank as it has been tampered with. Incidentally the garage told me the tank was rubbing on the chassis which resulted in the breach. My dealer quoted me £1800 for all the work to replace the tank and labour etc. etc. etc...... The welding is still holding. Good luck !!  People that say onions are the only vegetable that can make you cry obviously have not been hit on the head by a turnip