There are only a couple CK-4/SP's I've seen so far so most oil on the shelf is CK-4/SN & will have plenty additives. There may be a few CK-4/SN that may be more positioned for emissions reduction so will have less additives. Refer to the "Database" in this thread to go over your options. I would steer away from the CK-4/SP oils for now to answer your question.
CK-4 oil in your old Benz should be just fine. Additives have decreased since your 1990 Benz was developed & CK-4 style oil can help retain a good add packs totals. Knowing the T5 options you're either using the 10w-30 or 15w-40. Just know that a 5w-40 Euro could still be a good option. However, if you're concerned mainly about wear then a CK-4 will have more viscosity. While you may have to replace the cat eventually just due to age etc. it may be a small price to pay for getting adequate oil film protection. I don't know much about those old Merc's but I'd assume the cat is just pretty basic & wouldn't be too cost prohibitive to replace. There are folks on here that have run CK-4 oils in vehicles much newer than that & have said there are no known issues from its use. If you are using T5 10w-30 then a Euro 5w-40 could still be a good alternative. You have some variable options but Zinc is important for flat tappets & CK-4 will have more in general than a Euro oil will. Thanks
PC-12 is the next evolution that will come after CK-4 in 2027 & will bring a further reduction of additives.
Thanks for the explanation
when you say Euro 5w40 you mean something like this:
https://mag1.com/products/passenger...full-synthetic-european-5w-40-a3b4-motor-oil/
I am guessing these will still be API SN and would have less than 1000 ppm zinc and phosphorous in general correct?
What do you suggest in the Diesel CK4 .
I like these three and would like your opinion
1- Keep using Rotella T5 15w-40
2- switch to Liqui moly touring hitech diesel (API CG4) https://www.liqui-moly.com/en/us/to...RL8Ejc8SxjnD-ismOAGBKsQiXUAjQBqBZlibzjXW#2044
3- switch to Castrol GTX diesel 15w40 (I like the numbers from the database above, less detergent than the Rotella)