Fully synthetic engine oil.

I just used halfords 10-40 and she sounds spot on, '99 V reg.

Most synthetics do have inherently good cleaning properties but the leaking oil seal thing is quite rare. I started using Mobil 1 0W40 in an MX-5 engine (similar technology to the M13A, just a bit bigger) at 60,000 miles and it ran sweet as a nut until I got rid of the car years later. Never leaked or used any oil.

I put Mobil 1 5W30 in this last weekend. Noticeable difference in smoothness/vibrations and sound. Will be keeping an eye on fuel consumption over the next few fills.

Expensive, but happy with it.

Here's an article I've come across about oils. It explains synthetic oils quite well. Bit of a read though.. Might be a good idea to grab a cuppa before you start reading.
www.cafehusky.com/threads/what-kind-of-o...-and-how-much.31911/

The rules on what can be called "synthetic" are rather lax and oil with a small percentage of hydrocracked oils can qualify. Mobil 1 is generally accepted to be high quality, though. As a general rule, anything with a cold SAE viscosity of 0W will be a "real" synthetic.

Given the choice between 5W30 and 0W30, 0W30 is best (if available) because it flows better in a cold engine. ALL oils, even 0W, are too thick when cold and in many cases the oil filter bypass and/or pressure relief valve will be open (this is bad, because it means unfiltered oil and/or lower flow) until the oil has warmed up a bit. 0W reduces this time compared to 5W. At normal running temperature, only the higher figure (30) is relevant. 30 gives about 1mpg better fuel consumption than 40 but isn't the best choice for a high mileage engine where the clearances might be a little too wide.

i use the same oil in my 2002 jimny as in my 2005 type r fully synthetic castrol 5/w30
and now have been running the jimny on it for 2 n bit years