@RehanBhatti
Do not use SL....in fact do not use SJ too...When Suzuki is providing blend of SG and SM, why dont they are providing SL grade now? Reason is obvious They already know better that what machine they have produced and sold, what are their technical limitations and what they are producing now.
SL is much different than SG & SH...ZDDP is complete science..when Zddp contents are in discussion, it means various elements within Zinc Dialkyl Dithiophosphates where majors are Zinc(Zn), Phosphorus(P) and Sulphur(S)
Among three, Zinc and phosphorus were and are excellent anti wear additives.They are still available in reasonable quantities in Diesel Engine oils.
SG/SH API oil rating(Minimum ratings are written here while maximum is 1200-1300 ppm of Zddp)
Zinc = 1130 ppm (parts per million)
Phosphorous = 1120 ppm (parts per million)
SJ & SL oil ratings
Zinc = 1100 ppm (parts per million)
Phosphorous = 1000 ppm (parts per million)
SM API oil rating
Zinc = 870 ppm (parts per million)
Phosphorous = 800 ppm (parts per million)
Here, one can easily see the minute difference in Zinc constituent in zddp between SG & SL but major and considerable difference in Phosphorus constituent in ZDDP between SG & SL
From the introduction of API SJ in 1996, the API Classifications were more focused on the control of engine oil components that contributed to catalyst poisoning where one of the main contributors to catalyst poisoning was Phosphorus from ZDDP
So from API SJ on, there has been a move away from zinc based anti-wear agents, including limiting the phosphorus content of a PCMO to below 0.1% means 1000 ppm
SJ and SL have almost similar amount of Zinc but difference is quantity of Phosphorus and Sulphur(Issue is not only of Zinc)
API Classifications SL, SM and SN all contain reduced levels of phosphorus and sulphur, and therefore Zinc, for catalyst protection. You will have heard of “Low SAPS” (Low Sulphated Ash, Phosphorus and Sulphur) engine oils.
Of course there would be some differences between SJ & SL other than re-branding or Marketing techniques otherwise there was no need to redefine Classification in which SL is classified as different grade than SJ that's why usually SJ is referred for 2001 & older car while SL is referred for 2004 and olders(btw API is standardization body not any marketing body)
I have discussed and saw difference when during General checkup by Suzuki at their 3S dealers in Karachi, during free checkup day, my car was also selected for warranty checkup and without asking from me, they concluded and trained their staff that I was using non SG/SH higher grade. They compared other cars with of mine and some other cars and told although my engine was better cleaned inside(Surprisingly 
) but lacked required phosphorus & Sulphur in Zddp as i was not using Suzuki SG grade.
Zddp has this molecular structure which is obviously showing contribution of Phosphorus & sulphur in Zddp
