Ditto to Mark's list. I would add exchanging power steering fluid and changing the filter.

I've changed transmission fluid before on cars without a dipstick. You're correct in that you can measure the fluid drained out and replace that fluid. That's assuming that you can do a clean drain and capture all the fluid. Plus you'll have to account for clingage loss when measuring.

This'll get you by for the first change. The second time around you may want to have the level professionally checked.

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95 E320 Cabriolet, 169K