William,
My Engine Service Manual covers the Model 115.1 engine. It shows a picture of the power steering pump with a bolt near the top and one near the bottom. The instructions are:
1. Loosen fastening screws (1 and 2).[These are the bolt referred to above].

2. For tensioning V-belt, push power steering pump outwards by means of a lever.

3. Tighten fastening screws (1 and 2).

That's all.

Perhaps it is just lodged in place and is going to take a bit of prying to break it loose.

I realize this may not be much help, but it is what the MB manual prescribes.

Good luck.

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Ted
1979 240D