It's a short stroke 6 litre aluminum V12. Engine has 69,000 miles, chain driven SOHC's, 2.5 gallon sump, a big oil cooler and a big filter. The programmed shift points are at about 6300 rpm. I drive it 500-600 miles/year, so the oil only gets changed once a year, and it's due now. The prevailing attitude on the Jag lists is that the heat of the V12 mandates a thick oil, and that 10/30 is tantamount to homicide on the engine. I have been running Mobil 1 15/50, but I'm not necessarily sure that an oil this thick is warranted or even desirable. Jaguar specs 10/30, 10/40, and 10/50 for the spread from -4F to 104F, and, above 32F, then 15/40, 15/50, 20/40, and 20/50. It certainly gets below 32F here in Arkansas, and sometimes above 104F. I'm thinking that with this low mileage I want to be at the high end of 30 weight or the low end of 40 weight at most, and that for an engine that sits around a lot, moly would also be nice. The oil selection here is pretty limited. Here's what I'm thinking of changing to, in more or less this order: a. mix of Mobil 1 10/30 and 15/50, at maybe a 7:3 ratio; b1. Mystik SX8 10/30, a 30% PAO blend that is 12cSt; b2. a high mileage 10/30 like Pennzoil; c. Rotella synthetic 5/40 Mobil 1 0/40 and 0/30 is available here, but I have not seen the wunder Kastrol 0/30 and doubt it will ever be sold here ... Thanks in advance for any suggestions.