Was it mistake?
Now lot of those cars went above 200k and 300k miles. I bet good number of them on original fluid as MB USA keep the "lifetime" policy on ATF
Yet I have not hear about fluid related problem on those transmissions. Most problem is contamination of electrical cables when aging oring on adapter start seeping.
Since the first MY of W210 already passed 15 years mark, aren't we talking classics here?
I guess we'll never know. Maybe an error of judgement? I think you're right in that a lot of cars did go to 300k miles or more on the original fluid. It's the same here in Australia. Although I'd say you wouldn't notice the gradual deterioration in performance as you'd gradually adjust.
Actually it wasn't just MB. My last Ford had a 6 speed German ZF automatic transmission and Ford said that was filled for life and had no dipstick. That transmission was also electronically controlled and very sophisticated ... 6HP26 model. The common thing is they're both German transmissions. Apparently it was Ford who convinced themselves it was filled for life but not ZF. There have been many reported problems at around 150,000km-200,000km if they haven't been serviced. The same debate is being had on Ford forums in Australia about filled for life ZF's. And remember Ford in Australia stick these gearboxes behind powerful 5.4 litre V8's and turbo charged 4.0 litre 6 cylinder engines. There smallest and lowest powerd engine is a 4.0 litre non turbo 6 with 200kw. The turbo is pushing 300kw.
This is an excerpt from a motoring publication in Australia about filled for life ZF's:
The 6HP26 requires a special oil from ZF there are some oil manufactures that claim there fluid will work however unless its documented that it will work its recommended to use ZF oil. Now vehicle manufactures claim that the transmission is a “fill for life” or “Sealed Gearbox” however with research we have done we have found that ZF claim the Lifeguard 6 fluid is rated to 62,000 miles. See below details
“ZF Lifeguard Fluid, a high-performance lubricant specially engineered by ZF, gives customers a perfectly matched product. The transmission fluid reduces material wear, vibrations and noise for smoother shifting, extended maintenance intervals (100,000 km/62,000 miles), and maximum fuel savings.”
Transmission Rebuilders recommend servicing these transmissions every 60,000kms or 36 Months which every accrues first. It is also recommended on models with a one piece plastic sump to be converted with the more common steel sump with removable filter. The conversion cost about $70AUD more but then you will be saving $70 every service after that as you only need a filter and gasket rather than a complete sump.