I use Castrol Magnetec oil. Not sure what weight, but it is the MB recommended weight here in South Africa.

I dont have compression issues on any of the cylinders, it was tested.

How does the oil reach the lifter in this engine. Is it dedicted tubes, or groves/oil pasages? What could prevent the oil from reaching the lifter?

We dont have Marvel Mystery Oil her in South Africa. What does it do. I'm afriad of using engine flushes/detergents. Why? Well the MB service manger told me that they tried it once on a new AMG merc (not sure what model). The oil was replaced and it ran fine for a while. Without warning the whole engine siezed up. When they opened it up, they saw that some of the gunk (probably came loose after the flush action , i.e. while the fresh oil was inside) clogged up a oil passage. This limited oil to the engine pars and it seized up.