I haven't posted virtually anything on forums in a long time, couldn't pass this up because I've studied this subject so closely and found out so much in the last few years.
Good on you for wanting good synthetics in your custoer's cars, but begarding Amsoil's marketed "229.5" 5w-40; according to the Mercedes BeVo sheet online, the only MB sheet with Amsoil is 229.51 and it's for the oil that Amsoil is mis advertising and mis labeling as the stronger 229.5. As seen here:
Mercedes-Benz Specifications for Operating Fluids: Engine Oil, Gear Oil, ATF, Coolant, Brakefluid
Most of their synthetics only claim 229.1 equivalence and that's an old spec.
LIQUI MOLY 5W-40 LEICHTLAUF HIGH TECH (Part # 3863 or LM3863) from RM European is the best 229.5 deal going. Very high detergent and robust oil, I use it in my OM602A, M110, and father's Powerstroke 6.0. Audi and VW guys love it too.
Amsoil's universal ATF made my 722.413 stick and created the kind of symptoms the internet is full of, and required two full TC/pan drains to eliminate this aggressively thinning oil. Stick with Febi or Fuchs for ATF and PS fluid. Manual transmissions love Swepco, just like the Porsche guys swear. The only Amsoil product I use is for gasoline and called P.I.. It's not like I'm unwilling to pay for expensive oils, Amsoil is not expensive, considering I pay ~$30 for rear diff fluid from MB, while other's pay more for 75w-140 from Liqui-Moly for their BMW rear diffs. Why can't they get $30/quart?? It's not the 80's any more, Amsoil is living on fumes of glory and manufactured pride. Just know that most oils available now on the retail shelves are for ILSAC or Particulate Filter diesels, like "Delo 400 LE" sneaking into autoparts stores. Unless you have a particulate filter, only use the BeVo list for 229.5 sheet oils, it's what MB recommends for everything but commercial Direct Injection diesels (228.3/228.5 or 228.31 and 228.51 w/P.F.). Even Mobil has snuck in ESP as opposed to SHC on the BeVo list. Total has a North American deviation for their 8600 TIR which claims 16-TBN from Europe but wont be specific about it's formulation here. Schaeffer's 5w-40 is also a particulate filter oil. Delvac MX is a 228.3, the finest non-synthetic I know of available and loaded with good stuff. I've read more than one story of Rotella causing valves to stick in the cylinder head of younger Direct Injection engines with aluminum cyl. heads. Delvac 1300 is for particulate filters also. Again, my favorite is the above mentioned LM-3863, Hengst/Mann oil filter, and Dimple magnetic drain plug. Drain hot and often. If your valves are quiet, they need an adjustment to open up the tolerances to spec, thought mine was nice too until I adjusted the valves and could hear them again :-) Good luck everyone on the oil labyrinth.
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all my customers i put AMSOIL 5w-40wt European Car Formula into their gasoline cars.....it is specificly tailored to the additive requirements of high performance european engines....