I've seen the dipstick kits sold somewhere online which once again would easily enable you to check the ATF level in your "sealed" transmission. I'd do it in a heartbeat, wouldn't want to be kept in the dark about that.

I'm guessing MB decided to eliminate the dipstick in the first place because there where too many inexperienced "while you fill it up check under the hood" mechanics at gas stations eager to overfill, or add non-approved ATF, etc. Or maybe they just don't want anybody besides the dealer to touch that.

But bottom line is, the ATF needs to be checked, and replaced from time to time, along with the filter.

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W163 ML230 EURO SPEC 1999
W124 300E 1986