52100 steel has been around since before WWII. There have been some subgrades developed over the years for specialty applications, but the basic chemistry of the workhorse 52100 hasn't changed over the decades. The only thing that has changed over the years is the cleanliness of this steel and the precision used to machine the parts.

Yes, 1050 steel is sometimes used in bearing applications. It's an induction-hardening grade of steel, but that doesn't make it a bearing steel same as we think of 52100. We often use it in hubs where the race is machined right into the forging. There are many other grades of steel used in bearings. I've even seen ceramic rollers. But for this discussion nearly all automotive seperable races that are through-hardened are made of 52100 steel. Nobody's been able to come up with anything better.

When a lubed part fails and is sent to the dealership under warranty, it is often because of lack of maintenance, which is often obvious to the mechanic. The lab analysis simply quantifies and documents this fact. I'm sure most of us have read the horror stories of cars that come into the dealer for the 30K maintenance, and the mechanic finds the oil has never been changed! This is usually the point where a dealer will ask for a lube analysis. It's rare that a vehicle that has seen timely maintenance would experience a lube failure.

I highly doubt that synthetic lube in a differential would result in degradation of the unit. For diff lube, there is always some "synthetic" in the lube to carry the additives. It's really a question of how much of it is synthetic.

The believe the sequence of events, where somebody maintains their differential lube using a proper grade of synthetic, then has a failure under warranty, then has the mechanic send a UOA on the lube, then the lab discovers it is synthetic, then denied warranty because it is synthetic, is far and remote. The average person doesn't even think about their diff lube much less do something about it.

I'd be interested to see the product data sheet on MB grease. I'm sure it's fantastic grease. There are many others that are good and fit the application. Heck, I believe ExxonMobil has the best wheel bearing grease, better than their popular Mobil synthetic. It's called Infinitec 152. It's specially developed for automotive wheel bearing application. I have a 5-gal pail of it. It is not available over the counter. I doubt MB manufactures their own grease. Most companies - ours included - buy existing formulations and slap their company's name on it (and tack on a premium). There are only five manufacturing facilities in the US that make grease.

The reason the Alaskan Airlines plane went down was that the airlines extended the maintenance interval for the worm screw, not from wrong choice of lube or lube attacking the mechanism. The lube basically wore out and inspection wasn't often enough for that application.

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95 E320 Cabriolet, 169K