Mobile one is avail in 5-40,with the same specs as Lotus recomended oil. Send me 5$ + ups and I'll send you a quart. I am not an engineer,but if you go to the Amsoil site,I think you will see what I mean. But IMHO means IMHO. I do know that all AMGs come with mobile one from the factory,with instructions not to change the oil untill the Flexible service system tells you to(usually 10000-12500miles)seems a little too long to me,but I followed their inst. to the letter and have experienced no problems. One also has to keep in mind that Mercedes covers all maint untill 50000 miles--I have been told by a friend who IS an engineer and works for Toyota that the breakin proceedure is BS,but on the Lotus I followed that to the letter also to avoid problems with Lotus. The guy thought I was nuts.but,then he wouldn't have to deal with the engine warantee if it broke.
I use Amsoil in all of my cars,they have a marine oil (fully synthetic) which is great if you have cars which sit around a lot. NEVER had a problem.I think that Amsoil was the first fully synthetic oil,but they market it like Avon or Mary kay cosmetics, with 5 teir pricing,buy this amount and become a dealer,buy more,become a super dealer,etc. A great product ruined by poor marketing. When I was a kid I used to LOVE Kendall oil because it was green from the bottle,and I could never misjudge the amount of oil on the dipstick! I am quite sure that any full synthetic that meets Lotus specs,whatever the brand,would be fine,and would not void the warantee. :shrug: