I need more oil for the Defender, and it’s now to the point that I’ve been dreading. The Landy has been run on OMD90 (Oil Mineral Detergent), a military grade severe duty engine oil, since it was built in 1997, and my supply of said oil is now down to two litres. I need oil for an oil change, and while I can actually buy OMD90 directly from Fuchs, it’s £170 for 20 litres. Its closest match off the shelf is a part synthetic 10W40, which for Castrol Magnatec will cost me £5p/l, or Chevron ‘Supreme’ which will cost me £2p/l.

My question is twofold. Should I be considering changing to a different spec oil after almost 20 years of running OMD90, and if so, is Chevron ‘Supreme’ absolute shite or not?

Pic for reference.