Thanks.
However, it seems that the "could use 504" line in the manual would imply that the manual assumed something "better" on the sticker, i.e. 508 in the evo4 case. (Using 504 instead of 504 was a joke, not a typo.) Perhaps they just didn't bother pushing for 508 for gas mileage due to the low production numbers? (vs. the nearly identical engine now in the Atlas, which does get the 508 sticker.)
Even with the 508 standard existing purely to increase gas mileage, at the expense of longevity, aren't there advantages to the 504 standard vs. the 502? Anything possibly more important than the disadvantage of being thinner?
The main reason I remember for 504 over 502 with the EA888 gen 3 was carbon deposits; that problem hasn't changed wit the evo4, I assume.
The other way round: Now that the low-sulphur gas can be assumed ubiquitous enough to use 504 not just in fairly short OCIs, will a EA888 gen 3 that I've maintained with M1 502 gain anything (like magically decarbonized intake passages) from switching to 504 ASAP rather than using up the old 502?