Engines designed to meet Ultra Low emission standards or even Low Emission standards are (by default) much tougher on oil than earlier engines. The problem that Toyota had with their engines points this out. They reduced the size of the oil passages in the heads to make them run hotter (better for emissions but worse for reliability). What happened is that the differential in head temperature compared to the block was too great and caused gelling. This would not have been a problem with a base 4 or base 5 synthetic but it was with base 3 (petroleum) oils.

I suppose that if Toyota owners were as anal retentive as some of us about our Mercedes, they would have changed their oil more frequently and not had a problem even with the petroleum based oil.

Toyota wouldn't admit they had a problem but opened up the oil passages again and agreed to pay for gelling problems/repairs.

I'm still debating the purchase of a new E-Class. It's the engines I'm worried about. The design of these engines has been prioritized to reduce emissions and increase fuel economy at the expense of reliability.

Even with a capacity of over 8 quarts of synthetic oil, I would never go more than a year between oil changes. Since I drive a fairly low number of miles it's possible for the FSS system to wait up to two years before authorizing an MBUSA service!