Can anybody help?

I'm about to do an interim oil change (TDV6, first 8,000 miles) and was about to use Shell Helix Ultra 5/40, fully synthetic, which is what my stealer uses and recommended. When I went to get the oil I noticed there are two versions, one was for diesel and the other is what my stealer sold me for topping up, which I assume is a petrol engine version.

Does anybody know the difference and if it matters which one I use?

The primaray difference is in the additive pack. Oil that is blended for diesel engines has the ability to manage the ash content in the combustion process. The oil that is engineered for gas engines has anti foaming, viscosity extenders and other attributes necessary for its intended use. You should (need) to use the oil that is intended for your engine. While we are on the subject, oil needs to be replaced frequently if you intend to keep you vehicle for a long time. It is a myth that synthetic oil needs to be changed with less frequency. Whereas it is true that synthetic oil will hold up longer, it is subjected to the same punishment of mineral oil. The precise engine tolerances cause what is called shearing, this compresses the oil, which in turn breaks down its molecular structure. Additionally, the closed systems in today's engines contaminates the oil with the combustion by-products this will eventually cause sludge.

In summary, if your going to keep her, change the oil around 3K miles and use synthetic.

Did the oil & filter change last week. Used Castrol Magnetec A1 5 - 30. Drained the oil via the dipstick hole using a P.la vac pump, dead easy and clean. The filter was also easy to change after following the oil change thread on the Disco 3 site.

Anyway, since the oil change I've developed a very slight vibration in the cab on tickover., does anybody know what it might be? Could it be caused by the new oil making the tickover slightly faster. I only mean 100 rpm or so.