I have now decided on GC ("Formula SLX" over here, not to be confused with "SLX II Longlife") for my Xedos. I arrived at this decision because: - my Mazda Xedos manual recommends only a 30-wt whereas my wife's Mazda MX5 manual indicates that several oil grades may be used. Therefore I wonder whether this has to do with under-dimensioned oil passages in the Xedos V6. This view was probably influenced by reading about Mitsubishi FTO(?) V6s that can dry out their sumps if the oil is too thick to circulate at the correct rate. I have therefore decided to err on the side of (some would say extreme) caution. - There are any number of 40 & 50 wt oils available here (UK), but only very few 30-wts (no 20-wts at all.) - 5W30 is only available in various brands as ACEA A1 or A5 and I am have no reliable way of confirming that my engine can cope with this. The local Mazda dealership appears not even to understand viscosity ratings (told me M1 0W40 "is thinner than 5W30!") - The same applies to Saab 0W30 & Shell Ultra Helix 0W30, also available locally. - Cheapo 10W30 dino is available and would be acceptable (ACEA A2 or Ford WSD-M2C904-B2) but I would like to be able maintain the standard Xedos OCIs of 9k miles as the car does ~25k/annum. I don't trust these oils to hold up for more than 3k nor do I trust them to hold up under autobahn conditions (continuous WOT.) - GC was the only other available option that fitted the bill, being ACEA A3. So that is what I bought. It is unfortunate that GC costs >= £10/ltr unless a discount can be negotiated! Many thanks to all who commented on/answered my questions about this car's requirements in previous threads.