If your ball joints are original, then the rubber boots are probably cracked, which should allow you to get the oil into the joint itself with a small fill tube. I would use heavy gear oil like 90 weight differential oil and fill the ball joint up until it starts leaking out. It is easier to get to the ball joint if the front end is jacked up and the front wheels are off the ground. If you turn the steering wheel left or right it makes it even easier to access.

You said the car creaked when you turned the wheel. Have you tried to spray WD-40 into the steering damper strut that runs horizontally between the tie rod ends? There is a seal around the inner part of the strut that makes a creaking noise when it gets old. I had to replace mine because it creaked when I turned the wheel. It was not until I sprayed WD-40 into the strut that I realized it was causing the noise.

I would also hit the rubber sway bar bushings with WD-40 too eliminate that possibility.

Check that the vertical sway bar brackets are not broken as this could also make the noise you described.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles