Manual Altitude Adjusting Box 1975 W115 300D

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Hi all, I have found so much useful information on this forum over the years but this is my first post. I have a 1975 W115 300D that has a manual altitude adjusting box on the IP. I know that the IP itself is lubricated with engine oil but I'm not certain about the ALDA. When I remove to plug marked oil on top, the parts inside appear to be coated with what looks like engine oil but there isn't any oil level in the box. Is this correct? Is the ALDA lubricated with engine oil or should some type of oil be added to it?

My 17 year old daughter will be taking the car on a 2,600+ mile road trip next month and she'll need to make altitude adjustments along the way. I'm going through the car and getting it ready for the trip and I don't know enough about the mechanical ALDA. Thanks in advance