Regarding the chemistry, in real-world terms, practical effects, and science, what's the difference (if there IS a difference in "real-world" terms) between, say, Havoline SL 5W20 API SL and Havoline 5W20 API SM? I have no particular love for Havoline, other than the fact that it's always chatted up here and the fact that I bought 2 cases of the stuff on sale owing to M-1's RIDICULOUS price increases of late, and AA's recent sale price of 1.58/qt. Ok, ok, I like the Moly content and high flash point of the Havoline. It should easily go 5000-7500 OCI, right? My roller-skate 2005 Hyundai Accent GT 1.6 DOCH (10K total miles) specs 5W20 SL (no brand mentioned) with an option of 5W30 if 5w20 isn't "available". Of course, SL-rated 5W20 simply is NOT available. I bought a small 3 5-Quart jug stash of SL-rated M1 5W30 from Wally-World awhile back, but the scuttlebutt and what-not is that 5W20 is the best deal mileage-wise. So, what's lacking in SL vs. SM owing to EPA, manufacturer's specs, and the general cheapening of all things automotive? And, if I run the SM-rated oil, what's the additive pack (regarding VSOT 9big-time moly-add) and SLOB CD-2 big-time ZDDP-add), that I should put into the oil to bring the sub-standard (by all accounts) SM back to SL? Does ANY of it matter? Or am I just a knucklehead for even considering these issues (I suspect i'm a knucklehead , but not any more than the rest of you!)?